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THE FUNDAMENTAL LAWS OF 

HUMAN BEHAVIOR 

Lectures on the Foundations of any 
Mental or Social Science 

by 

MAX MEYER 

] 

Professor of Experimental Psychology 
in the University of Missouri 




RICHARD G. BADGER 

THE GORHAM PRP:SS 
BOSTON 



\ 



Copyright V.UU by Richard 0. Badger 
All rights reserved 



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The Gorham Press, Boston, U. S. A. 

gClA303116 



CONTENTS 

PAGE 

Lecture 1 1 

Being, doing, thinking. Thinking of humanity 
in terms of thought. The subjective and the ob- 
jective. Consciousness and nervous function. The 
nervous system compared with a telephone system. 
Designing a nervous system. Sensitivity, con- 
tractility, conductivity. Differentiation of tissues. 
An analogy of tissue conductivity. Deformation 
of the body bringing about change of its situation. 
Avoiding an obstacle. The story of the snail. A 
nervous system of impossible design. 

Lecture 2 16 

Contraction at a point other than that of stimu- 
lation. The moth and the light. A steady stimu- 
lus causing a periodic motion. The need of a 
nervous system proportional to the development 
of special motor organs. Sensory and motor 
points of the body. Nervous connections represen- 
ted graphically by arches. Cells the biological 
elements of structure. A nerve cell not a cell but 
a part of a cell. Neuron, fiber, ganglion cell. 
Types of neurons. Collaterals. Terminal arbor- 
ization and dendrites. White and gray matter. 
Relative unimportance of the ganglion cell for a 
theory of mental life. 

iii 



iv CONTENTS 

Lectures 30 

Locomotion of the jelly-fish. Concerted action 
of all the divisions of the body and local respon- 
siveness. Need of a gradation of connections dif- 
fering in resistance. Corresponding points. Re- 
sistance dependent on length of conductors. Con- 
nections of non-corresponding points. Impossible 
manner of connecting the neuron arches. First 
improvement of manner of connection: One-way 
valves at the meeting points of neurons. Second 
improvement: The connections between the arches 
being themselves arches consisting of three neurons 
each. 

Lecture 4 46 

Reflex arches. Their peripheral and central points. 
Central sensory points and central motor points. 
Central points of a lower and higher order. Let- 
tering of diagrams explained. Central sensory and 
central motor neurons. Reflex and instinct. In- 
stinct a selecting and collecting agent. Overflow 
of a strong sensori-motor discharge into the most 
closely connected arches. The source of motor 
power different from the signal for its expenditure. 
What a nervous excitation can be likened to. 
Signaling by rods and levers or by pneumatic 
tubes. Velocity of signal very great, but not 
infinite; not dependent on intensity. A neuron 
likened to an electric storage element. A simple 
picture of a nervous process needed for our imagi- 
nation of nervous function. 

Lecture 5 59 

Advantage of comparing the nervous process 



CONTENTS v 

with a process of streaming. Analogy of the jet- 
pump. The whole nervous system permeate: d by 
any nervous process, but not with uniform intensity. 
Suction at motor points; openings made at sensory 
points. Velocity of the relief of tension. Condi- 
tions of the intensity of streaming at any definite 
point of the system. Exhaustion. Resistance 
increasing with, and even more rapidly than, the 
flux. Overflow not identical with universal per- 
meation. The selective function of an instinct ex- 
plained by the principle of deflection, the collective 
by that of overflow. 

Lecture 6 69 

Tension of the total muscular system not inter- 
fering with special activities. The motor point 
not identical with the point that is moved. Rel- 
atively fewer reflexes, more instincts in higher 
animals. The compounding of nervous elements 
into groups, of these groups into larger groups, and 
so on, into a single nervous system. The nervous 
system of a worm. Nerve centers. Lower and 
higher centers. The nervous system of a crayfish. 
The brains of fish, frog, bird, and mammal. The 
nervous system of man. The cerebral hemi- 
spheres of man. 

Lecture 7 85 

Learning. The susceptibility of nervous con- 
ductors. Variations of the nervous path. (1) 
Two kinds of variation of response. (2) Sensory 
condensation. (3) Motor condensation. Grace- 
ful motion. Inhibition. How a child comes to fear 
the fire. 



vi CONTENTS 

Lecture 8 98 

Substitution of a direct for a devious nervous 
path. Nervous tension inducing growth. Auto- 
matic action. Periodic levels of learning. Two 
meanings of forgetting. Positive and negative 
susceptibility of neurons. The curves of learning 
and forgetting. 

Lecture 9 110 

Sensory condensation in piano playing. Propor- 
tional reduction of the resistance of higher and 
lower centers connecting the same corresponding 
points. The positive (and negative) susceptibility 
of a higher center greater than that of a lower center. 
Motor condensation in grasping. 

Lecture 10 120 

Order of acquisition of the first four classes of 
habits. Control of the sense organs of the head. 
Direction and extent of the fixation movement of 
the eye. Improvement by experience of the fixation 
movement of the eye. A variation of response re- 
sulting from a close succession of nervous processes 
just as from a deflection of one by another. Co- 
ordination of the eyes. How an infant learns to 
face a sounding object. Control of the hands and 
arms. Learning to raise the arm in response to a 
visual object above the eyes. Loose co-ordination 
of eye and hand. 

Lecture 11 138 

Control of the feet. The ability to walk equal 
to rising plus balancing. Reflex of straightening 
the legs. Reflex of squatting. Balancing with 



CONTENTS vii 

hand support preceding free balancing. Balancing 
on one leg preceded by balancing on both. Walk- 
ing not a simple instinct, but a compound of re- 
flexes united largely by experience. Balancing 
sideways preceding balancing fore-and-aft. Stretch- 
ing the foot reflexly toward a thing which impresses 
the eye. Locomotion resulting from this reflex. 
Creeping. Creeping on two legs preceded by 
creeping on one. Influences of creeping on walk- 
ing. Sitting up. Finger-sucking superseded by 
other habits. Free standing rarely preceded by 
walking. One-sidedness and general clumsiness of 
first walking. Encouraging a child to stand: a 
purely negative event. The so-called instincts of 
constructiveness and destructiveness : rather habits. 

Lecture 12 153 

Repetition of motor activity characteristic of 
learning in childhood. Variation of the order of 
earliest accomplishments. Speech organs: whis- 
pering and singing. First speech sounds. General 
and specific resistances of neurons. The motor 
outlet of a group of successive nervous processes 
determined by the temporal order of the qualita- 
tively different processes. The general resistance 
as well as the specific resistance reduced by any 
special flux; but the reduction of the specific resist- 
ance outlasting that of the general resistance. 
Possibility of a particular distribution of specific 
resistances resulting from experience. 

Lecture 13 168 

A simple sensory excitation bringing about a 
temporally complex response. Some, but by no 



viii CONTENTS 

means all, temporally complex responses to a simple 
sensory excitation explainable on the basis of 
geometric-mechanical rivalry of motor organs. 
Multiform variation of response. Importance of 
kinesthetic sensory activity. Two stages in the 
development of speech. Reflex pointing and utter- 
ance of a dental sound. Left-handedness during 
the first months of life. Right-handed reflex 
pointing. Right-handedness and speech. Ac- 
cented and gesticulating languages. 

Lecture 14 181 

Spatial perception. Inherited responses to 
spatial form. Acquisition of unitary groups of 
conductors serving all objects of the same design. 
Mutual attraction of nervous processes of equal 
strength. Melody and harmony. Two kinds of 
tonal similarity. Neurons applying their specific 
resistance in various degrees to a variety of pro- 
cesses. Rhythm equals subjective grouping of 
objectively uniform excitations. Habits of per- 
forming group motions consisting of one effective 
and (one or) several preparatory movements. No 
counting in rhythmical perception. Why all com- 
mon rhythms are of the doublet and triplet kind. 

Lecture 15 196 

Imitation. Auditory and visual imitation at 
different stages of life. Kinesthetic imitation not 
inherited; of little importance even when acquired. 
Emotional reactions. Either contraction or relaxa- 
tion prevailing in either organic or skeletal muscles. 
Emotional reactions inherited. Emotional reac- 
tions either of direct or of indirect value, for ex- 



CONTENTS ix 

ample, as signals for social interaction; especially 
in primitive man and in animals. Civilized man, 
deriving little benefit from his emotional reactions, 
practically unable to control them by experience. 

Lecture 16 211 

The speech function serving as a generalizing 
function. Abstraction a kind of generalization. 
Advantages of the written language in generaliza- 
tion for individual use and for communication. 
Science the sum total of all those generalizations 
which mankind has tested and collected. Written 
symbols becoming a class of (artificial) objects to 
which man learns to respond as formerly he learn- 
ed to respond alone to the objects of nature. Arith- 
metic. The generalization "force" in mechanics: 
a creation of man like all other generalizations. 
Advantage of handling words rather than things. 
Danger of speculation. 

Lecture 17 227 

The generalizing function changing from a ner- 
vous and muscular into a purely nervous function. 
Relation between processes in the higher nerve 
centers and strictly subjective experiences. Ner- 
vous functions of generalization especially likely to 
have also the subjective aspect. For the generaliz- 
ing nervous function in another person 's brain we 
substitute an imaginary mental state. The ner- 
vous correlates of sensation and imagery. Associa- 
tions of successive and of simultaneous mental 
states. Attention. Pleasantness and unpleasant- 
ness. Insufficiency of introspective psychology. 



ILLUSTRATIONS 

FIGURE PAGE 

1 An impossible nervous system 6 

2 Simplest motor response of a snail 9 

3 Snail turning 11 

4 Snail avoiding a rock 11 

5 Neuron arches 21 

6 Growth of a neuron 23 

7 Types of neurons 25 

8 Collaterals 26 

9 Ganglion cell 27 

10 Nervous system of a jelly-fish (acalepha) 31 

11 Nervous system of a jelly-fish (hydromedusa). . . 35 

12 Impossible manner of connection 39 

13 Imperfect manner of connection 40 

14 One-way valves 41 

15 Imperfect manner of connection 45 

16 Nervous architecture: Neuron arches and their 

possible connections 46 

17 Possible modification of details in nervous archi- 

tecture 46 

18 Possible modification of details in nervous archi- 

tecture 64 

19 The bulk of the nervous system of an earth-worm 71 

20 Low and high centers: Group formation in the 

nervous system 73 

21 Nervous system of a crayfish 78 

22 Brain of a fish; double view 79 

23 Brain of a frog; double view 80 

24 Brain of a bird; double view 81 

25 Brain of a lower mammal; double view 81 

xi 



xii ILLUSTRATIONS 

26 Nervous system of man; double view 82 

27 Brain of mtai; double view 84 

28 Burnt child fears the fire 93 

29 Automatic action: Short-circuiting in the ner- 

vous system 102 

SO Steps in acquiring skill: Periodic levels of learn- 
ing 104 

81 Learning dependent on time 106 

32 Forgetting dependent on time 107 

38 Forgetting immediately after practice 108 

34 Sensory condensation explained Ill 

35 Thumb and finger movement 116 

36 Learning how to grasp 118 

37 Fixation movement of the eye 122 

Simultaneous innervation of antagonistic muscles 124 

89 Improvment of the fixation movement of the eye.. 126 

40 Co-ordination of the two eyes or any two organs 130 

41 Raising the hand 134 

4*2 Motor response dependent on temporal order of 

stimulation 159 

13 An acquired distribution of specific resistances. . . . 165 

44 Multiform variation of response 170 

15 A simple stimulus calling forth a temporally com- 
plex response 172 

46 The simple perception of space 182 

VI Sensory points serving form stimulations 183 

18 Spatial stimulation with inherited response... . . . 184 

19 How the habit of rhythm may be acquired 191 

50 Tension of facial muscles in joy or anger 204 

51 Relaxation of facial muscles in disappointment. . 209 

52 Naming takes the place of handling 212 

53 Handling takes the place of talking 212 

54 Generalization without actual speech 228 

55 Two directions in successive association 236 



PREFACE 

THE complete dependence of all human activity 
on the functional properties of the nervous 
system and on the changes which these functional 
properties undergo during life, is much empha- 
sized in innumerable treatises written by physiologists 
and psychologists. Yet the way in which these changes 
come about is described in such vague, subjective terms, 
that the changes, the "education" of the nervous system, 
appear to the young student as mysterious, as miraculous, 
as unreal, almost incredible, after the reading of these 
treatises as before. Let me quote from such a treatise 
by a distinguished physiologist — very admirable and very 
convincing provided one is convinced even before reading 
it — the following sentences: "As a result of experience, 

definite tracks are laid down in this system. The candle 

flame injures the skin once when the finger is brought 
into contact with it. The one act of injury which has 
followed the first trial of contact suffices to inhibit any 
subsequent repetition of the act. " Such a description of the 
matter does not clarify it to the young student, but merely 
substitutes for the mystery which from ancient times has 
surrounded it, another mystery clad in modern terms. 
"Experience" is spoken of as if it were a concrete reality, 
a powerful agent producing changes, instead of making 
it clear that experience is only an abstract name for the 
very fact that these changes occur. "Injury" is said to 
inhibit an act, but the student is left to look in vain for an 

xiii 



xiv PREFACE 

analogy among the objective realities he knows, where an 
injury received by machinery results in the reversal of 
its motion. A stick of dynamite placed on a rail certain- 
ly docs not cause a locomotive to stop, the next time, 
before touching it. The mystery can be removed from 
human activity only by offering the student concrete, al- 
though perhaps hypothetical, images and uniting these into 
a syStCm no more complex than the machinery which 
moves about him everywhere in his every-day life. 

To make clear the functional changes which occur in 
Hie nervous system and which, determining the indi- 
vidual's life activity, are of tremendous importance to the 
individual and to society, it is necessary and customary 
to use diagrams of the nervous system. I have used such 
diagrams of my own design in this book too. I am pre- 
pared for hearing from anatomists and perhaps even 
from physiologists and psychologists the judgment 
that my diagrams look queer, that they do not reproduce 
what one sees in the dissecting room with and without a 
microscope. I confess that I have committed this sin 
with the full conscience of what I am doing. It is custo- 
mary, in the diagrams which illustrate nervous functions, 
to imitate the actual curving of the nerve fibers passing 
from the spinal cord to the brain and here from lobe to lobe. 
Hut I am convinced that this is not only unnecessary, but 
even harmful. In this book the diagrams illustrating 
function have been entirely separated from those illustrat- 
ing anatomy, and the former have been designed exclusively 
with a view towards making clear the fundamental laws 
of learning. However queer they may look to the anato- 
mist, they will be the more useful to the student of human 
activity for whom this book is written, because they will 
free him of the tendency to burden his mind with irrelevant 
curves resulting from mere accidents of growth. 



PREFACE xv 

What this book proposes to do is essentially an inves- 
tigation into the problem contained in the following ques- 
tion: What are the simplest assumptions, necessary and 
sufficient, to explain hypothetically the facts of human 
behavior as dependent on the function of the nervous 
system? Having answered this question, it attempts 
to illuminate the deep-rooted habit of describing human 
behavior as dependent on subjective states, on states of 
consciousness, — a habit which still largely governs the 
sciences of human society, preventing them from throwing 
off the shackles of subjectivity. 

My thanks are due to my wife for aid and advice in 
preparing this book; and to my assistant, Mr. A. P. Weiss, 
who drew the illustrations, for his devotion to this work. 

M. M. 



FIRST LECTURE 

Being, doing, thinking. Thinking of humanity in terms 
of thought. The subjective and the objective. Consciousness 
and nervous function. The nervous system compared with a 
telephone system. Designing a nervous system. Sensitivity, 
contractility, conductivity. Differentiation of tissues. An 
analogy of tissue conductivity. Deformation of the body 
bringing about change of its situation. Avoiding an ob- 
stacle. The story of the snail, A nervous system of im- 
possible design. 

WHEN we meet one of the things which 
surround us in nature, we ask, perhaps 
more frequently than any others, one of 
these three questions : What is it? What 
does it do? What are its thoughts? We know many things 
with respect to which the first is the only question we ask. 
We pass through a street which is being paved. When we 
are told that the blocks of stone put down in regular rows 
by the workmen, are granite, we are probably entirely 
satisfied. But when we approach a mill and see the 
wheels turning, we are not satisfied when we know only 
that it is a mill. We desire to know what it does, for 
example, whether it is likely to injure us if we step nearer, 
or whether it can do special work which we need to have 
done. When a cow or bull crosses our path, we are again 
not satisfied if we know only the animal \s name. We are 
much concerned with the animal's action. Will it compel 

1 



2 III MAX BKHAYIOR 

us to change our direction, or can we safely remain where 
we are? When, thirdly, as school children, we are with 
our teacher iu the class room, we are greatly interested, 
not only in what he does, but still more so in what he 
thinks. If he thinks well of us, we are glad. But let us 
raise the question how we know whether our teacher 
thinks well of us or not, and we must admit that we can 
not directly know his thoughts, that is, have his thoughts any 
more than he can have our thoughts, — that we know it only 
through our observations of what he does in giving us 
things, in writing what we may read, in speaking what we 
may understand. Yet if we are asked whether we are 
chiefly interested in our teacher's acts or in his thoughts, 
we are probably quite ready to assert that we regard his 
thoughts, the existence of which we can not directly know, 
but only assume, as of far more importance to us than his 
acts, which we do know directly. In this apparent con- 
tradiction lies in a nutshell the problem with which we 
have to deal in this book. Why do we think of humanity 
almost exclusively in terms of thought, although our 
experience contains no other person's thought, but only 
his behavior? Many other examples could be used to 
show that a person's thoughts, which nobody can have 
but himself, are nevertheless of the greatest concern to 
ot hers who can not know them, can not have them. When 
parents send their children to school, they send them in 
order that their intellects may be trained, their characters 
developed. Let us inquire what is meant by such words 
as intellect and character. The dictionary tells us that 
they refer to thought processes, not to particular activities 
or to a person's appearance. The most important train- 
ing then, which every parent strives to give his child, is a 
training of his powers of thought, of this mysterious 
unknown, 



BEING, DOING, THINKING 3 

Not infrequently we hear people speak of brain work 
and of manual labor. We hear them distinguish between 
brain workers and those who work with their hands. 
The distinction seems quite acceptable. Of course, those 
who use these phrases do not mean that they know much 
about the workings of the brain. They simply mean 
that certain persons, although they do not do much 
which can easily be seen, are nevertheless active in that 
they think. They work mentally, as we say. And for 
this mysterious unknown they often receive a high salary. 

Very common is this emphasizing of thinking, this 
complete or relative disregarding of an individual's doing 
or being, in ethical valuations. A boy has placed a plank 
across the street car track and derailed the car. He tells 
us that he thought that the foundations of the bridge a 
little distance away had been washed out and that he 
intended to stop the car and save our lives. Whatever 
may be the facts in the case, that is, the doing and the 
being of the water, the bridge, the car, and the boy him- 
self, — we probably praise him for his thoughts and inten- 
tions. Or, the boy tells us that he wished thus to injure 
and punish another boy whom he saw as a passenger on 
the approaching car. Whatever may, again, have actually 
happened, visibly and audibly, — for the boy's thoughts 
we have only contempt, we call them wicked. Yet the 
boy's being and doing is the same in both cases: he looks 
the same and he has placed the same plank in the same 
manner across the track. It is again this mysterious 
unknown, his thoughts, which concerns us chiefly. 

The most conspicuous example, perhaps, is to be found 
in religious doctrines and ideals. Not good works, but 
faith decides the test which the Christian has to undergo, 
according to the Apostle. Not what man does, or what he 
is, gives him his religious qualification, but his faith, 



I HUMAN BEHAVIOR 

that is, his thoughts, again this same mysterious un- 
known. 

In Done of these examples arc anyone's thoughts 

known to, that is, had by, any one other than himself. 
Even an Inquisition, which has power over life and death, 
is unable to find out what is thought by those whose 
religious or irreligious thoughts it pretends to investigate. 
It can find only what is done by them, including, of 
course, under doing what is written and spoken. 

For more than two thousand years a science has existed 
which has devoted itself to the mysterious unknown 
which we have just characterized by examples. One may 
give it the name of mental science, or, rather, mental 
sciences, for in our modern times science is breaking up 
into many branches, according to the diversified interests 
of mankind and in consequence of the limitation of 
individual mental capacity. Until quite recent years these 
mental sciences were based upon the conscious experiences 
of the individual who "professed" the science, upon 
introspection. During the last few decades the convic- 
tion became general that a science of the subjective, an 
introspective science, because of its limited possibility of 
generalization, hardly deserved the name of a science. 
In order to remedy the defect which had been discovered, 
objective methods, like those used in the physical sciences, 
were introduced into the mental sciences, to supplement 
(he subjective method of introspection. In the following 
pages we shall attempt to study by objective methods 
the tnosl fundamental objective facts which are related to 
subjective phenomena, and as comprehensively as possible 
to make clear this relation between objective facts of 
being and doing and the subjective experiences of our own 
thinking. 

No other fact concerning the relation between the 



THE SUBJECTIVE— THE OBJECTIVE 5 

subjective (the individual consciousness) and the objective 
(the world of the natural sciences) can be more impressive, 
than that consciousness seems to be entirely or, at least, 
relatively dependent on, conditioned by, the function 
of an individual's nervous system. So generally is this 
recognized, that even the extreme assertion that con- 
sciousness is impossible without the existence and function 
of a nervous system, wT>uld undoubtedly find a majority 
of votes among scientists. 

This will justify — if for the present such a justification 
seems necessary — our beginning with the study of the 
nervous system's significance for the being and doing of 
those objects in nature which are known to possess a 
nervous system. 

We may compare a nervous system with the telephone 
system of a city or even of a nation, which enables a 
person to give orders in one place and have them received 
and executed in another. A nervous system consists 
essentially of an immense number of string-like structures, 
very fine and relatively very long, just as a telephone 
system consists essentially of a large number of conducting 
wires. However immense the number of these strings may 
be, they are never found as a disorderly mass, but always 
arranged according to definite rules. For the sake of 
understanding clearly the significance of their architectural 
arrangement for the behavior of an animal — we know that 
all those things in nature which possess a nervous system, 
and even many without it, are called animals — let us 
imagine that we have the duties of a creator and that we 
have to furnish a given animal with a nervous system of 
our own design. How, then, should we systematize, that 
is, put together into a unit, all the strings which we are 
to insert into the animal's body? The simplest plan 
seems to be that of uniting all the strings so that one of 



(i 



HUM AX BEHAVIOR 






the two ends of each string is located in a single point of 
the body, whereas all the other ends are left unconnected 

and are distributed among the various parts of the body, 
like 4 the diagram of Figure 1. Suppose we offered an 

Center 




17 * a I i 

Fig. 1 — An impossible nervous system. 

animal which has thus far been without a nervous system, 
a nervous system of this design. Should the animal be 
grateful for our gift? Would this gift be helpful to the 
animal in its struggle for life? 

In order to answer this question, we must first gain 
some insight into the life, the being and doing, of an 
animal which possesses no nervous system. Let us make 
ourselves familiar with the behavior of a simple animal 
which we all greatly admired in our childhood days, the 
snail. It is true, the snail does have a rudimentary kind 
of a nervous system. But the snail is anatomically so 
simple thai it could almost equally well get along without 
it. Thai snail, then, of which we shall now speak, is 
indeed only an imaginary snail but near enough to reality 
to serve as an example for the demonstration of certain 
general laws of animal behavior. 

We recall that among the main properties of living 
matter are sensitivity, contractility, and conductivity. 



DESIGNING A NERVOUS SYSTEM 7 

In the lowest forms of animal life every particle of the 
body shows all three of these properties about equally. 
In the higher forms of animal evolution this is quite 
different. Our muscles, for example, have but little 
sensitivity and conductivity. At the expense of these 
two the third property has been so much increased that 
the muscles may be called the contractile tissue of our 
body. In such a case we speak of the differentiation of 
tissues. Muscular tissue has become differentiated from 
the rather uniform tissue of lower forms of life, just as 
in modern society the individual has become differenti- 
ated and can, for example, make excellent shoes, but no 
clothes to cover the other parts of the body, whereas the 
undifferentiated savage makes tolerably good clothes for 
himself as well as shoes. 

Differentiation of tissues is, of course, not restricted to 
the one kind just mentioned. Other tissues lose most of 
their contractility, but become the more capable of con- 
ducting any process which happens to go on in one point 
of them to all their other points. This does not mean 
that the velocity with which the excitation travels in 
them becomes much greater. Analogies from physics and 
chemistry make it fairly certain that the velocity of 
conduction, the velocity of the current, remains about 
the same. But the resistance of the conducting tissues 
becomes much less. Such tissues are the nervous tissues, 
those strings of w T hich we spoke above and about which we 
shall have to say much more further on. The main 
property of nervous tissue is its conductivity, by which 
the strings are capable of serving like telephone wires 
conducting electric currents. It is important that, in 
thinking of increased conductivity of tissues, we do not 
think of increased velocity of conduction. While we need 
not deny that the velocity of conduction may be somewhat 



8 HUMAN BEHAVIOR 

affected by this differentiation, what we mean chiefly is 
thai the excitation is offered less resistance by the nervous 
tissue than by any other tissue, that it travels through 
nervous tissue, not more quickly, but certainly more 
strongly, more effectively than through the non-conduc- 
tive tissues. 

Other tissues, again, differentiate in such a manner that 
they obtain a highly increased sensitivity at the expense 
of their other properties. Think of the ease with which 
we find our way on a dark night when, during new moon, 
only the stars aid us with their faint light. The sensitive 
elements on the retina, the background of our eye, respond 
even to this faint light and stimulate the nerve ends 
which, through their conductivity, enable the various 
parts of the body to execute the proper movements. 
These three properties, however, sensitivity, contractility, 
and conductivity, are by no means the only properties of 
living matter. They are merely those properties which 
chiefly concern us in our present study. In addition, 
there are many other properties of less importance for our 
present purpose. If we desire to know more about them 
and the various ways in which tissues differentiate, we 
must consult the text-books of the sciences which are 
devoted to these problems, namely, histology, the science 
of tissues, and biology and physiology, the sciences of 
the function of living matter. 

We mentioned that the main property of the string- 
like elements which make up the nervous system, is their 
conductivity. Let us now apply this knowledge to our 
problem of the acceptability or non-acceptability of the 
gifl which we offered to our imaginary, nerveless snail. 
There is, according to our assumption, and, indeed, 
practically in accordance with the actual facts, no differ- 
entiated tissue in the snail's body. Each particle is 



TISSUE CONDUCTIVITY 9 

sensitive, each particle contracts when stimulated, and 
each particle conducts what goes on therein to the neigh- 
boring particles, causing the same process in them. 

Suppose, now, the snail, spread out over the ground 
as when creeping, is very gently touched at the point of 
the tail end marked in Figure 2. Owing to its sensitivity, 




Fig. 2 — Simplest motor response of a snail. 

the tissue touched responds. Being contractile the 
tissue responds by contracting, so that the tail assumes 
an unsymmetrical form like the one shown in possibly 
exaggerated manner by the dotted line in Figure 2. The 
excitation, first caused in the part touched, spreads in 
consequence of the conductivity of the tissues. What this 
conductivity means may be made clear by an example taken 
from ordinary experience. If we drop a small quantity of 
syrup into a glass of water, we can see how it gradually 
spreads through the whole fluid until the chemical con- 
stitution, different just after the drop fell, again becomes 
uniform all through the fluid. When we speak of an 
"excitation" caused in a tissue by a touch, this means, 
too, that the chemical constitution of the point touched 
has been changed and that this change tends to spread 
wherever it can, until the constitution has again become 



10 HUMAN BEHAVIOR 

uniform everywhere. This spreading is meant when we 
speak of the conductivity of the tissues. The excitation, 
then, spreads from the contracted part to all the other 
parts of the animal's body. Wherever it reaches, con- 
traction of the tissues occurs. But, naturally, just as the 
syrup spreading out through the water becomes more and 
more dilute at the starting point, so the excitation spread- 
ing out through the body becomes weaker and weaker 
at the starting point. Finally, perhaps after a second or 
two, the intensity of the excitation has become quite 
uniform all through the body, and the contraction, the 
density of the tissues, has also become equalized all through 
the body. Only the deformation of the body surface and 
a weak uniform excitation and contraction of the whole 
body remain as the effect of the touch. 

Now, the chemical state which we have called excita- 
tion, means the presence in the tissues of chemical sub- 
stances which are not normally there. It is natural, then, 
that the forces which are always active in living matter 
will tend, after the external influence has ceased, to bring 
about such spontaneous chemical changes that the normal 
condition is restored. Gradually, therefore, the normal 
chemical constitution of the body returns, and as it 
returns the state of contraction disappears. The body 
expands again. However, since the previous contraction 
had become practically uniform in a deformed body, the 
expanded body, having regained its normal shape, no 
longer has its previous situation. The deformation by 
the sudden shrinking occurred on one side; the reformation 
of form by expansion occurred on all sides of the body. 
Its axis has slightly turned in the direction indicated by 
the two arrows perpendicular to the axis of Figure 3. 

The application of the few and simple facts which we 
have just learned, at once reveals their great importance. 



DEFORMATION OF BODY 11 

We desired to gain some insight into the life of an animal 
which possesses no nervous system, in order to answer 
the question whether a particular nervous system with 





Fig. 3 — Snail turning. Fig. 4 — Snail avoiding a rock. 



which we intended to furnish the animal, would be an 
acceptable gift to the animal or not. The most important 
activities of an animal are plainly those of protection 
and of nutrition. Let us see if w r e can comprehend the 
behavior of our snail when it is either in search of food 
or avoiding an injurious object. 

Suppose the snail is creeping on the ground in the 
direction of the arrow I in Figure 4. Let us take the 
mechanics of locomotion in the forward direction for 
granted, so that we may take up at once the more special 
problem which concerns us here. The snail, creeping 
forward, approaches the stone which accidentally lies in 
its way, and the right side of the head comes into contact 
with the stone. (For simplicity's sake we assume that 
our imaginary snail has no tentacles.) We know now, 
from our previous discussion, what must happen. The 
part which has been excited by the touch of the stone, 



12 HUMAN BEHAVIOR 

contracts. A little later, expansion of the body occurs, 
hut expansion not only of the part near the stone but of 
all the body with practical uniformity. The result is a 
change of position. The axis of the snail now assumes a 
position more nearly that of the arrow II. The internal 
conditions — whatever they may be — which caused the 
original forward movement, again become effective. The 
snail, moving forward, perhaps again comes into contact 
with the stone. The same happens as before. The axis 
again turns toward the left. Again the forward move- 
ment begins and now, perhaps, is continued without 
touching the stone; the actual path being approximately 
that indicated by the solid line. 

All this is by no means an extraordinary event in the 
animal's life, an unusual kind of behavior. It is prac- 
tically the complete story of the snail. The snail, in 
order to live, must eat. Lack of food, continued for some 
time, results in chemical changes in the body. In conse- 
quence of structural and functional properties of the 
body which we cannot study here, these chemical changes 
bring about a forward movement. A rock (or any other 
obstacle) lies in the way. If the rock could permanently 
stop the forward movement, the snail would starve to 
death. But, in one or several stages, a change of the 
situation is brought about by a change of the direction 
of the animal's axis. Now the snail creeps on. Other 
obstacles which may be encountered are taken in the 
same way. On its forward march the snail, by accident, 
sometime passes over edible substances, which stimulate 
flic mouth organs and, consequently, are consumed. 
Later, lack of food brings about locomotion again, and 
the same things happen in the same cycle. 

One may feci inclined to exclaim: An animal's life 
cannot be so simple, so automatic as that, — dependent 



THE STORY OF THE SNAIL 13 

on the mere accident that food substances should be in 
its fortuitous path ! But why not? It is true, many a snail 
will fail to come across any food substances and die of 
starvation. Such is life! But enough will have better 
luck and live to propagate the species, for food adapted 
to the needs of snails is common on earth. 

Not only food is obtained in this — if one wishes to call 
it by that name, mechanical — way; protection against 
injury is thus made possible too. If the snail instead of 
approaching a rock, had come near a directly injurious 
substance, it might have changed its route even before 
touching that substance; for the tissues of its body are 
excited, not only by touch, but also by many other in- 
fluences, for example by a change of temperature, or by 
the effect of a volatile chemical substance. A piece of 
camphor instead of a rock would have turned the snail 
some distance before touch would have been possible. 
Another important method of protecting itself is that of 
completely retiring within its shell. This again requires 
no additional mechanism. We supposed above, that 
the touch of which we spoke was a very gentle touch. It 
will, of course, always be gentle if it results from the 
snail's — this slowly moving animal's — own motion. If 
the touch is relatively strong, as when a child touches 
the snail with a straw, the excitation resulting and spread- 
ing with great force all through the tissues must cause, 
not only the tissues at the point of contact, but also the 
neighboring tissues, possibly all of the body, to contract 
vigorously. If the whole body contracts strongly, it 
must, since a part of it is attached to the interior of the 
shell, necessarily disappear in the shell. It is to be noted, 
however, that one kind of behavior is impossible in this 
kind of an animal, namely, stimulation occurring at one 
point of the body and contraction occurring exclusively 



14 HUMAN BEHAVIOR 

at an entirely separate point of the body. There must 
always be what may be called a wave of both excitation 
and contraction, spreading from the point of stimulation 
more or less — so little, indeed, in some cases that contrac- 
tion may seem to be confined to the point of stimulation, 
or so much in others that clearly the whole body is in- 
volved. But the point of stimulation can not in any 
case fail to be included in and to be the center and starting 
point of the wave of 'contraction. Nevertheless, a snail 
does not need a nervous system in order to live. It can 
behave in the way in which we have described it as be- 
having without possessing nervous tissues of any kind 
whatsoever. 

Nevertheless we may wish to appear generous and offer 
our snail the nervous system of our design in Figure 1. 
Although the snail can get along without a nervous sys- 
tem, why should it not get along even better when in 
possession of our gift, we might naively ask. Imagine 
the snail had accepted the gift and were approaching the 
rock in Figure 4. The moment when the contact occurs 
one of the peripheral ends of the nervous strings is excited. 
The strings are so differentiated that they have an im- 
mensely greater conductivity, that is, lesser resistance, 
than the undifferentiated tissues. The excitation, there- 
tore 4 , is conducted to the point where all the nervous strings 
arc connected and thence with great intensity of flux along 
all the nervous strings, thus reaching effectively all the 
parts of the body. Consequently, all the parts of the 
body contract practically at the same time with great 
force. A prompt and relatively strong contraction at 
the point of stimulation, followed slowly by a weak and 
uniform contraction of the w r hole body is no longer possible. 
The resulting change of position is also impossible. The 
whole body contracts and, after a while, expands again, 



AN IMPOSSIBLE NERVOUS SYSTEM 15 

to touch, of course, the rock in exactly the same way- 
that it did the first time. In consequence of the touch, 
the whole body contracts again. It expands again, con- 
tracts again, expands again, contracts again, and so on 
ad infinitum, until the animal is either exhausted or 
starved or both. Any way of avoiding the obstacle is 
impossible. It is clear, then, that the snail would be very 
much worse off with this kind of a nervous system than 
without any. Without any nervous system it can live 
quite well, unless it happens to have exceedingly bad 
luck. With this nervous system it can not live any more 
than a human being could live who, whenever he saw or 
heard anything, instead of normally responding to the 
situation presented, would invariably have an epileptic 
fit, a violent and entirely useless unadapted muscular 
contraction. 



SECOND LECTURK 

Contraction at a point other than that of stimulation. 
The moth and the light. A steady stimulus causing a 
periodic motion. The need of a nervous system proportional 
to the development of special motor organs. Sensory and 
motor points of the body. Nervous connections represented 
graphically by arches. Cells the biological elements of 
structure. A nerve cell not a cell but a part of a cell. Neuron, 
fiber, ganglion cell. Types of neurons. Collaterals. Ter- 
minal arborization and dendrites. White and gray matter. 
Relative unimportance of the ganglion cell for a theory of 
mental life. 

LET us consider, quite apart from any special 
problem, in what manner and for what purpose 
strings conducting like telephone wires could 
be serviceable in an animal's body. It is plain 
from the foregoing that they are needed only in case the 
contraction is to occur not at all at the point of stimula- 
tion, but at some other point. This can be brought 
about only by conducting away the excitation from the 
point of stimulation by string-like tissues which cannot 
themselves contract, but possess a greater conductivity 
than ordinary, undifferentiated tissues. Carried to an- 
other point, the excitation can there cause the contraction 
desired. This kind of function is necessary in all the 
more highly organized animals. Take 4 an insect, a moth 
for example. We know that the most striking behavior 

16 



THE MOTH AND THE LIGHT 17 

of a moth is its flying towards any source of light. 
This is the result of the nervous connections between 
the wings and the eyes. The right eye is connected 
(if not exclusively, at least better) by nervous strings 
with the muscles of the left wing, the left eye with the 
muscles of the right wing. If the moth has the source 
of light on its right side, the right eye receives more light 
and consequently a stronger excitation than the left eye. 
The left wing then beats the air more forcefully than the 
right wing, and the axis of the animal is turned to the 
right until both eyes are excited by the light with equal 
intensity, that is, until the moth flies directly towards 
the light. 

We need not discuss here the question as to the value 
of this instinct (instinct is the name given to such con- 
nections between sense organs and motor organs) to the 
moth. We may take this value for granted in spite of 
the fact that millions of moths are destroyed because of 
this instinct of flying toward the light. Sources of light 
destructive to moths on the surface of the earth are a 
very recent invention of mankind, for which nature 
cannot be expected to have made provision in giving the 
moth its biological inheritance. It is not difficult to 
imagine that this flying in the direction of more strong- 
ly illuminated or lighter objects rather than of darker 
ones aids the moth in obtaining food. So much is plain 
that it could do a moth, whose anatomy is (relatively) so 
highly developed, no good whatsoever if an excitation 
caused by light in the region of the head would cause a 
contraction of the tissues located in the same place. In 
order to be of any value to the animal it is necessary that 
the chief sensory areas, the eyes, and the chief motor or- 
gans, the wings, be connected with each other by different- 
iated tissues of the conducting kind, by nerves. 



18 HUMAN BEHAVIOR 

It may not be amiss, even at the danger of getting a little 
side-t racked, to discuss another fact which is of great 
significance for the behavior of animals. We said that 
the movement of the moth's wings was caused by the 
excitation occurring in the eye. The question may be 
asked: How can a rhythmical movement like that of the 
flapping wings be caused by a continuous excitation like 
that in the moth's eye? We have no need to explain 
this here in detail, but it is important to point out, that 
such a transformation of something continuous into 
something discontinuous is an exceedingly common 
occurrence in nature. It is especially important to note 
that it occurs in the inorganic world, the dead part of nature, 
as frequently as in the organic world, in living nature, so 
that we cannot be accused of having neglected the possible 
claims for recognition of any so-called vital or mental 
forces when we simply stated that the wings flapped 
merely because of light falling steadily on the animal's 
eye. Let us take from the inorganic world a few examples. 
The wind passing steadily over the surface of the ocean 
does not cause, by friction, simply a motion of the surface 
water in the same direction and a compensatory move- 
ment of lower layers of water in the opposite direction. 
It causes, as we all know, a motion of the particles of 
water which takes place, only to a slight extent in the 
horizontal direction of the wind, mostly in a vertical 
direction, up and down, causing waves which periodically 
rise and fall a considerable height. Or, when we blow a 
whistle steadily, the result is a rhythmical movement of 
the particles of air enclosed in the whistle, a physical 
sound. When water flows very slowly from the faucet 
in our kitchen, it does not fall in a continuous and very 
narrow stream, but in periodical drops. Air blown under 
water through a tube, similarly rises in periodical bubbles. 



PERIODIC MOTION 19 

Nobody thinks that such a transformation in these cases 
requires any hypothetical vital or mental forces. To 
assume any such forces in the case of muscular activity 
is equally unnecessary. What we have said about nervous 
excitation in the eye causing rhythmical motion of the 
wings is really all that need be said, unless we are specially 
interested in the details of physiological science. 

Let us return to our problem as to the kind of a nervous 
system which could be regarded as an acceptable gift by 
our snail or any other animal. We saw that only one 
kind of behavior is impossible to the snail without a ner- 
vous system, namely, a contraction at one point of the 
body in response to an excitation started at a different 
point, without any contraction occurring at this latter 
point, or at least, without a contraction occurring at the 
point of stimulation with any force approaching that 
of the contraction at the former point. For example, if 
the tip of one of the tentacles of a snail — let us think of 
a snail with tentacles — is affected by a certain stimulus, say 
fire, it might be safer for the animal to respond by a 
strong backward movement of its locomotor organs, 
however far these are from the point of stimulation, than 
to respond strongly by a contraction of the stimulated 
tentacle and weakly by action of the locomotor organs. 
We see at once the close connection between the existence 
of a nervous system and of highly developed special or- 
gans, especially of locomotor organs. Higher animals, 
having legs, must indeed, because they have these special 
organs, respond to stimuli occurring at certain excitable 
points of the body by a forward movement of the legs, 
to stimuli at other excitable points by a backward 
movement of the legs, and by no other motor reaction. 
The snail, which has scarcely any specialized motor 
organs, just on this account does not absolutely need 



20 HUMAN BEHAVIOR 

a nervous system. So much nervous tissue as the snail 
possesses, serves minor purposes which do not much con- 
cern us here. 

On the other hand, if an animal has specialized loco- 
motor and other motor organs, fins, wings, or legs, with 
double sets of muscles, for forward and backward motion, 
its nervous system must be designed according to the 
following plan and can not be designed in any other way 
without defeating its purpose. Certain excitable points 
of the body must be connected by conducting strings with 
certain contractile tissues located in definite points of the 
body; other excitable points must be connected with 
certain other contractile tissues of the body. If we 
simplify our way of expressing this, we may say: Each 
sensory (that is, excitable) point of the body must be con- 
nected by a conducting string with a definite motor (that 
is, contractile) point of the body. Let us remember, how- 
ever, that the facts are not quite so simple as they are 
expressed in these words. Actually, a single sensory 
point is scarcely ever excited in isolation, and a single 
contractile point, a single muscle fiber, never contracts 
while all other fibers remain at rest. However, general 
statements of fundamental facts for the purpose of re- 
membering and reflecting upon them in the abstract, are 
always artificially simplified. Otherwise they would be 
of little value to our thought, which is limited in capacity. 
All scientific laws, even the greatest and most famous of 
them, are artificial simplifications. This justifies, then, 
our speaking of the connection of one sensory point with 
one motor point as if such a simple nervous connection 
wen 4 possible. 

We may represent such nervous connections graphically 
as in Figure 3. Each sensory point S is connected with 
a motor point M by a conductor, represented in the figure, 



SENSORY AND MOTOR POINTS 21 

of course, by a line. That this line has the form of « 
flat arch is not essential. This special form of the diagram 
has been chosen here because of its convenience, which 
will later become even more evident. Since there are a 



Se Sd Sc Sb Sa Mai Mb he lid Me 
Fig. 5 — Neuron arches. 

great many sensory and motor points, the diagram ought 
to contain a great many arches. In our figure they are 
all represented by only five. They are drawn one above 
the other because this is the most convenient form of 
drawing them, not because any such connections are 
likely to be actually found in a similar parallel arrange- 
ment. The difference in size of the arches is also a mere 
matter of convenience, without any actual meaning. If 
no other assumptions are made at any later time, we shall 
always regard the arches as representing nervous con- 
nections of the same length. 

Let us at once apply this diagram. We spoke above 
of the instinct of a moth of flying toward the light. Take 
S b to be the right eye and S c the left eye. Of course, an 
eye is not a single sensory point, but since it functions in 
this case as a unit, there can be no objection to speaking 
of it and representing it graphically as if it were a single 
point. Take M b to be the left wing's muscles and M c 



22 HUMAN BEHAVIOR 

the right wing's muscles. Again we understand that the 
muscles of a wing are not a single motor point. The 
muscles of one wing are, indeed, two sets of muscles, so- 
called antagonistic sets, of which one serves the upward, 
the other the downward movement. Each of these 
muscle sets consists of thousands of muscle fibers. One 
fiber or a small group of these fibers may be called quite 
correctly a motor point of the body. However, since the 
whole double set of muscles functions together, brings 
about the definite effect, the flapping of one wing, we may 
speak of it here and represent it graphically as if it were a 
single motor point. The wonderful instinct of flying 
toward the flame is then represented graphically, simply 
by S b being connected with M b but not with M c , and S c 
being connected with M c , but not with M b . 

Having understood the all-pervading importance of 
these conducting strings for the behavior of all more 
highly organized animals, it is natural to seek for some 
more detailed knowledge about their growth, their struc- 
ture, and their function. 

The smallest structural elements of which both animal 
and vegetable organisms consist have for about a century 
been called "cells." This means literally boxes — we 
have a box under our house which we call a cellar. The 
name appears less strange to us on knowing that those 
structural elements which were first discovered by means 
of the microscope happened to look like little boxes. 
These were plant cells. It was, of course, soon found that 
no I all vegetable elements of structure are box-like. Some, 
for example the long and thin flax fibers used for the 
manufacture of linen, do not resemble a box. But the 
name cell had already been adopted by the biologists as a 
general name for elements of structure and was now applied 
also to those elements to which it was not applicable in 



NERVE CELLS 23 

its literal meaning. It was equally applied to the elements 
of structure in the vegetable and animal kingdom, and 
the whole living world was — and is — said by the biologists 
to consist of cells. Accordingly the strings, which serve 
as conductors for excitations in the bodies of higher animals, 
ought to be called cells, — for t the sake of distinguishing 
them from other kinds of cells, perhaps nerve cells. Such, 
however, is not the case. The term nerve cell has come 
to mean, unfortunately, something different. We shall 
at once see what and why. 

In its most undeveloped form an individual unit of 
nervous tissue is a small, almost spherical body (Figure 6, 



Fig. 6 — Growth of a neuron. 

a). As this body grows it becomes pointed in one or 
more places and sends out a string-like prolongation, 
which continues to increase in length (Figure 6, b, c, and d) 9 
so that it may become easily a hundred thousand times 
as long as it is thick, reaching a total length of several 
feet, whereas its thickness is always microscopical. The 
original little ball from which the string grew out, con- 
tinues then to exist as a relatively thick swelling of the 
string. We must remember, however, that it only looks 
thus, that it did not originate as a swelling of the string. 
Being relatively bulky, it is not difficult to understand 
that this thickened part of the string should have attracted 
the interest of investigators before the exceedingly fine 



24 HUMAN BKIIVVIOR 

string. When it was first the object of biological research, 
its belonging as a part to the long and fine fiber was over- 
looked. It was studied as an individual thing, and the 
name cell, generally applied to the elements of biological 
structure, was applied, instead of to the whole fiber with 
its swelling, to the swelling alone, which was called a 
nerve cell. So the inconsistent use of the word cell in its 
application to nervous tissue, referred to above, came 
about and is still almost universal. 

In more recent years a new, unambiguous terminology 
has been adopted, which we shall use in the following. We 
shall call the whole structure, the fiber with its swelling, a 
neuron, the fiber without its swelling simply fiber, and the 
swelling alone a ganglion cell. The use of the word 
ganglion cell is explained thus: In nervous tissues gray 
looking masses are frequent which, on microscopical 
examination, reveal themselves as accumulations of 
swellings with the contiguous pieces of their fibers. It 
is as if we had a large number of ropes each having a 
knot somewhere and had taken all these knots in one of 
our hands. What we then have in our hand might be 
compared with the accumulation of swellings just men- 
tioned. Such a mass of nervous tissue has long been 
called a ganglion. Now, it is a peculiar biological fact 
that these swellings of neurons are not found simply here 
and there in isolation, but that they are always found in 
groups, sometimes not very large, sometimes very bulky, 
— these very ganglions. Since the swellings of the neurons 
are always found in ganglions, they have been given the 
name of ganglion cells, which we shall adopt here. 

Many are the forms in which the neurons present 
themselves. Figure 7 shows an assortment of them. 
The swelling may be at one of the ends as in the case of 
a and r of the figure, or away from either end as in the 



NEURONS 



25 



case of b, d, and e. The long fiber may split into two 
fibers as in c, or even into more. The swelling may 
happen to occur just at the point of the division of the 




b C d e 

Fig. 7 — Types of neurons. 



string. In this case the neuron looks like d. The string 
may in its course turn sideways, form a kind of loop, 
and continue from the turning point in the original 
direction. If now the swelling happens to be at the place 
of the loop, the neuron must look like e. In all these 
varieties of form we find the same structure, a string with 
a swelling. Some years ago, when the interest of the 
histologists was still in the main restricted to the ganglion 
cell, various kinds of such cells were distinguished accord- 
ing to the number of long fibers which they sent out, and 
called unipolar (a), bipolar (b) and multipolar (d) cells. 
Since the ganglion cell has ceased to be regarded as an 
element of structure in the former sense, these distinctions 
and names have practically lost their significance. The 
neuron is essentially a string capable of conducting an 
excitation from one end to the other. All structural and 
functional properties are necessarily subservient to this 
end of conduction. 



26 HUMAN BEHAVIOR 

Certain features of the neurons, which are not shown 
in Figure 7, should still be mentioned. We said that the 
long fibers sometimes split into two fibers. Another 
breaking up of the fiber may occur in a manner similar 




Fig. 8 — Collaterals. 

to the way in which a river takes up large tributaries. 
Long fibers may enter the main fiber as in Figure 8. The 
tributaries, which most commonly form with the main 
fiber angles of approximately ninety degrees, are called 
collaterals. But still another feature of the neurons is 
to be mentioned. Each ending of a nervous string looks 
somewhat like the frayed-out end of a thread. The end 
breaks up into a large number of relatively short branches, 
the so-called terminal arborization (Fig. 9, at a). In 
case the swelling of the neuron happens to be located at 
one of the ends of a neuron, these small branches must 
naturally come out of the swelling itself. The neuron 
then looks like Figure 9. The branches proceeding from 
the swelling are called dendrites, which is a Greek name 
meaning about the same as the Latin name terminal 
arborization, namely tree-like branchings. In Figure 9 
a neuron is represented whose main fiber is relatively 



STRUCTURE OF NEURONS 



27 



short, almost shorter than the dendrites. This shortness, 
however, is not the rule, but rather the exception; the 
main fiber, often also called the axis cylinder, usually 
greatly exceeds the dendrites in length. 

There is frequently a difference in coloring between 
the parts of a neuron. The ganglion cell looks dark, the 




Fig. 9 — Ganglion cell. 



fibers lighter. This has given rise to the distinction of 
white and gray matter in the brain — gray matter taking 
its name from the presence of numerous dark ganglion 
cells among the fibers. The popular view, however, of 
the greater importance of the gray matter than of the 
white matter is a superstition. 

The ganglion cells have a delicate interior structure, 
and even the fibers are not simple, but possess an interior 
structure, so that they may be said to consist of fibrils. 
About the functional significance of these inner divisions 



28 I UMAX BEHAVIOR 

of a neuron too little is at present definitely known. The 
questioo as to the function of the ganglion cell and the 
fibrous parts of the neuron must be answered at present 
in a manner very different from that which was customary 
fifty years ago. It was then often asserted that the 
ganglion cells were the residences of ideas, each little 
box the seat of one idea, so that the total mental capacity 
of a person might be determined by counting the number 
of his ganglion cells. It is now recognized that an idea 
can not be said to have its seat anywhere. The ganglion 
cells do not have any more direct relation to our mental 
life than the conducting strings. On the contrary, we 
shall see that we can fairly well understand our mental 
life without any reference to the ganglion cells. Their 
physiological significance is probably, in the main, only 
of the following two-fold kind. The ganglion cell is the 
point of vegetation, so to speak, from which all growth 
proceeds, and it is the storehouse from which the neuron 
in any emergency can quickly draw the means of sub- 
sistence. We have seen that the whole string of a neuron 
grows from a little sphere. This sphere continues to 
exist even after the neuron with all its ramifications has 
obtained its full development, and is then the ganglion 
cell of the neuron. If growth is necessary later, because a 
branch of the neuron has been cut off or otherwise de- 
stroyed, new growth proceeds from that point of the string 
which is farthest from, but still connected with the gang- 
lion cell. On the other hand, if a conducting string is 
continually used for hours, changes in the appearance 
of its ganglion cell occur which probably indicate changes 
of a chemical nature, called by the physiologists signs of 
fatigue. It seems that the string, in order to serve con- 
tinuously for a long time as conductor of an excitation, 
needs to be resupplied with certain chemicals, and that 



SIGNIFICANCE OF GANGLION CELL 29 

these chemicals are kept in store for the string within the 
ganglion cell, which, because of its size, is less quickly 
exhausted than the string. Whether the ganglion cell 
has any significance in addition to those functions just 
mentioned, seems doubtful. 



THIRD LECTURE 

Locomotion of the jelly-fish. Concerted action of all 
the divisions of the body and local responsiveness. Need of 
a gradation of connections differing in resistance. Corres- 
ponding points. Resistance dependent on length of con- 
ductors. Connections of non-corresponding points. Im- 
possible manner of connecting the neuron arches. First 
improvement of manner of connection: One-way valves at 
the meeting points of neurons. Second improvement: The 
connections between the arches ■ being themselves arches 
consisting of three neurons each. 

WE have stated that the fundamental 
principle upon which the design, — the 
architecture, so to speak, — of the nervous 
system is based, is the following one. 
Each sensory point of the body is connected by a con- 
ducting string with a definite motor point of the body. 
The selection of a suitable motor point for connection is 
nature's proper business to which she has attended during 
a long process of evolution of the animal race. Every 
animal is born with fully developed connections of this 
kind, or, at least, with rudiments which by heredity are 
predetermined to grow into such connections during the 
individual's early life. If an animal is born without 
them, life is impossible. 

However, it is easily seen that a nervous system of this 
extremely simple kind will need improvement as soon as 

30 



CONCERTED ACTION 31 

the animal race which possesses it makes progress from 
the most primitive to a somewhat higher organization of 
its bodily functions. Let us consider an example. A 
jelly-fish of the kind called acalepha still has an exceed- 
ingly low organization; yet it will make clear what we 
wish to understand. For locomotion it has a bell-shaped 
body, so that, on contraction of the bell, the whole body 
moves through the water in the direction of the closed 
end of the bell. When seen from the front the bell looks 
like Figure 10. On the periphery of the bell there are 




Fig. 10 — Nervous system of a jelly-fish (acalepha). 

eight points (one of which in the figure is marked S). 
From each of these points conducting fibers similar to the 
fully developed neurons in higher animals pass into the 
neighboring tissues, but not far enough to come into 
actual contact with the fibers radiating from any other 
point S. The purpose of these fibers is clear; they con- 
duct any excitation occurring at any point of the rim 
with but slightly diminished effectiveness to all the 
tissues of that eighth-division, causing thus a uniform 
response of the whole division to any stimulus applied to 
any one of its points. In addition to these one fiber 
seems to pass from each S in the direction of the center 
of the bell. For what purpose? Obviously, to make it 
more certain that during the process of locomotion no 
division of the bell lags behind the others in contraction. 



HUMAN BEHAVIOR 

It is plain enough that no straight-way locomotion would 
result if, for example, the tissues on one side of the rim 
would contract when, having lagged behind, all the 
diametrically opposite tissues are still in expansion. 
This lagging behind, however, would frequently occur. 
To understand it readily, let us imagine the analogous 
case of eight leaky places on a water pipe. Suppose the 
frequency of the dropping at each place to be about the 
same, say, one drop a second. But even then we could 
not expect all the drops to fall simultaneously, eight fur- 
ther drops to fall again simultaneously after a second, and 
so on. The eight drops would fall in a quite irregular 
succession. Let us make the application to our case. 
The rhythmical contraction would be caused by the 
chemical constitution of the jelly-fish at the time in 
question, when perhaps no food has been taken for some 
time and locomotion thus has become necessary. The 
chemical constitution being about the same in all divisions, 
no division would have a frequency of periodic contraction 
differing much from that of any other division of the 
body. Nevertheless, the contractions would not occur in 
the eight divisions simultaneously any more than the 
falling of the eight drops spoken of above. But this 
simultaneity could be easily insured by connecting the 
eight divisions by conductors. Now, as soon as one of 
the divisions spontaneously begins to contract, this con- 
traction causes an excitation in the nervous plexus of 
that division. This excitation is carried to all other 
divisions and at once all other divisions begin to contract. 
This connection of all the divisions of the body would 
work beautifully if no other kind of locomotion were ever 
needed than straight -way locomotion in response to an 
internal stimulus, the chemical constitution of the body 
at the particular time, for example, some time after the 



LOCAL RESPONSIVENESS 33 

last taking of food. But frequently external stimuli act 
upon the body and require, not a straightforward loco- 
motion, but a change of direction as response. For 
example, the jelly-fish, while swimming, strikes a rock 
with one side of the bell. The jelly-fish then must change 
its direction. That division which touched the rock 
must contract more strongly than any other, especially 
than the diametrically opposite division, in order to bring 
about the change of direction. Without conduction, the 
predominance of the action of the one division touched 
would be certain. But with perfect conduction to all 
other divisions it would be equally certain that no such 
predominance of a local reaction, no local responsiveness 
to an external stimulus would be possible. Here is, 
then, the necessity of a compromise. And this compro- 
mise is effected by having the eight radial fibers not join 
in the center, but stop short before reaching each other. 
Thus undifferentiated tissues, tissues of high resistance, 
are interposed to weaken the excitation coming from one 
of the divisions to such an extent that only one division 
can react strongly to the external stimulus. All others 
react only weakly. 

One must not think that for a concerted action of all 
divisions of the bell, like the action of straightforward 
locomotion, string-like conductors of differentiated tissue 
are indispensable. The various divisions of the rim of 
the bell might force each other into the same periodicity 
and, what is still more important for our present considera- 
tion, into the same phase of periodic contraction through 
the ordinary conductivity of the undifferentiated tissues. 
Whatever division is at any moment the first to contract, 
mi^ht send its excitation by means of conduction through 
the undifferentiated tissues to all the others and thus 
e the whole rim to contract at the same time. This 



34 HUMAN BEHAVIOR 

is t ho more possible when the periodic contraction of each 
particle is nol the result of an external stimulus but, as 
we have seen, the result of a chemical constitution at any 
given time practically uniform throughout the whole 
body. The stimulus coming from one division, not 
having to cause, but only to hasten in all the others the 
contraction which would have occurred a little later any- 
way, need be only weak. Nevertheless, the question 
remains if it would not be too weak if it had to pass wholly 
through undifferentiated tissue. Nature, therefore, must 
make the radiating conductors just long enough to meet 
this condition of reducing the resistance just eioughfor 
concerted action; but not the least longer, for every in- 
crease of their length is equivalent to cutting down the 
local responsiveness without which the animal could not 
survive. We understand thus why the radiating fibers 
do not join in the center. 

It is interesting to note that compromising, which is 
the very foundation of all social life of animals, of all 
social institutions of mankind, is found to be an essential 
function in the individual life of any one of the very lowest 
animals w T hich possess a nervous system. The unity of all 
organized nature, which is the fundamental concept of 
modern biology, is exemplified by this role played in any 
life, low or high, by compromises. Two conflicting con- 
ditions seem to make life impossible. But the problem 
would be hopeless only if a complete denial of the demands 
of either the one or the other were insisted on. On the 
oik 4 hand, concerted action calls for the most perfect con- 
duction from any division of the rim of the bell to all 
the others. On the other hand, local responsiveness calls 
for the interposition of high resistances between the 
diametrically opposite divisions of the rim. The com- 
promise musl then consist in this, that all the divisions are 



A COMPROMISE 35 

connected by conductors, but in such a way that conduc- 
tion from one point of the rim to opposite points is by the 
properties of the conducting medium itself more resisted 
than conduction to neighboring points. Nature has, as 
we saw, solved the problem by stopping the differentiated 
radiating conductors as far short of the center as the 
condition of local responsiveness requires, leaving in the 
center enough undifferentiated tissue interposed to meet 
this requirement. Another way of fulfilling the condition 
of varying resistance is by resorting to the length of the 
differentiated conductors without interposing any un- 
differentiated tissue. There can be no doubt that the 
length of a nervous conductor determines its resistance 
as the length of telegraph and telephone wires determines 
their resistances. The longer the conducting string, the 
greater its resistance. Nature has solved the problem 
in this way in another kind of jelly-fish, called hydromedu- 
sa. Here all the points of the rim are connected by differ- 
entiated conductors forming a ring, as shown in Figure 11. 




b -— a 

Fig. 11 — Nervous system of a jelly-fish (hydromedusa). 

If any division of the rim contracts, the excitation is by 
this ring conducted to all other divisions. But the excita- 
tion reaching opposite divisions of the rim is much weaker 
than that which reaches neighboring ones, in accordance 
with the varying length of the conductor. This difference 
in the intensity of the conducted excitation does no harm 



36 HUMAN BEHAVIOR 

in the case of ordinary, straightforward locomotion. The 
rhythmical contraction is in this activity the result of the 
chemical constitution of the body which, perhaps, has 
been the result of lacking food for some time. This 
chemical state differs but slightly in the various parts of 
the body. The different divisions of the rim, therefore, 
would contract and expand in almost the same periodicity 
anyway. A very slight excitation conducted from else- 
where is then sufficient to hurry up any division which 
without this excitation would lag behind. But when a 
stimulus acts from without on any point of the rim, only 
those divisions are caused to respond strongly to the stimulus 
which are in the neighborhood of the stimulus. The 
other divisions of the rim, receiving a weaker and weaker 
excitation the longer the piece of the rim over which the 
excitation has to travel, are considerably affected only 
in the neighborhood of the point of stimulation. The 
divisions opposite this point remain practically unaffected 
by the stimulus. 

Let us glance back again at Figure 10. We said that 
(1) the radiating fibers help to prevent the lagging behind 
of any division in the ordinary activity of locomotion. 
The figure makes it clear that any excitation is more 
effectively conducted between any divisions by the help 
of these fibers than it could be conducted through the 
undifferentiated tissues. (2) The local responsiveness is 
retained by the radiating fibers stopping short before 
reaching the center of the bell. For example, if S is 
stimulated by an external influence, the excitation is 
carried also to a, b, and c, but more weakly to a and b 
and very much more weakly still to c. In order to reach 
c the excitation has to pass from the radiating fiber S to 
the radiating fiber c over a rather long step of undifferenti- 
ated tissue. Undifferentiated tissue has a much higher 



GRADATION OF RESISTANCES 37 

resistance than nervous tissue. Consequently, the ex- 
citation reaching the points, a, b, and c, is more and more 
weakened, and no interference with the local responsive- 
ness at the point S can appear. If the radiating fibres 
did unite at the center of the bell, a, b, and c would 
all be equally excited. The problem of universal con- 
nection of all parts of the body by conductors of low 
resistance, combined with undisturbed local responsive- 
ness, can therefore be solved architecturally in more than 
one way. Figures 10 and 11 represent two solutions of 
the problem, both found in nature. But the solution of 
Figure 11 is the more perfect one, because the universal 
communication through conductors is more perfect, while 
local responsiveness is as satisfactorily retained as in the 
other case. 

The example of the jelly-fish has taught us that one 
kind of nervous connections w T ithin the animal body is 
not sufficient. There must be many kinds, — or rather, 
there must be a gradation of connections differing in the 
resistance offered by the conductor in the various cases. 
If it is desirable for an animal's well-being that an ex- 
citation occurring at a certain point, say A, be followed 
most readily by a contraction at the point a, the points 
A and a must be connected by a conductor of small 
resistance. Let us call those points which are thus 
connected corresponding points, in order to have a brief 
term by which we may refer to them. If, as in the case 
of a jelly-fish, these corresponding points A and a are 
practically identical, the conduction is a self-evident 
fact even without any special conductors. If, as in the 
case of the moth, A is an eye and a the muscles of a wing, 
the conduction between the corresponding points must be 
mediated by a nervous string, or chain of nervous strings, 
of the shortest length possible under the anatomical 



38 HUMAN BEHAVIOR 

conditions. But all — or at least some — of the other 
(non-corresponding) contractile points of the body must 
also he in sonic way connected with the point A. Other- 
wise, no concerted action would be possible. The jelly- 
fish would, for example, be scarcely capable of swimming 
straight ahead; the moth would hardly be able to alight 
on a twig or leaf which happens to impress itself on the 
moth's eye and towards which the moth must act, not 
only with its wings, but also with its legs. These further 
connections with the point A, however, in order to leave 
the connection A-a in its proper functional order, must 
have a higher resistance, — as we have seen, must be 
longer than A-a. 

In higher animals, whose tissues are all differentiated 
to perform special functions, the nervous connections are 
practically all connections between sensory and motor 
points, that is, between points of the body which are by 
differentiation specially sensitive to particular physical 
or chemical influences, and points which are of differenti- 
ated contractile tissue. It is true that nerve fibers are 
also found to end in tissues which are not contractile; in 
glands, for example. However, these cases are the 
minority, and may be left out of the discussion here, 
since w r e are especially and directly interested in behavior 
only, which depends, of course, on the function of con- 
tractile 4 tissues, of muscles. We have represented in 
Figure 5 the short — or direct, as we may say — connections 
between corresponding sensory and motor points in the 
shape of arches. We must now find a way of representing 
graphically those nervous conductors which lead from 
each sensory point to those motor points w r hich are not 
corresponding. These conductors must be, as we have 
found, longer than the conductors directly connecting 
corresponding points. It is clear, then, that we could not 



IMPOSSIBLE MANNER OF CONNECTION 39 



represent the conductors connecting non-corresponding 
points as they are represented in Figure 12. This figure 
is shown here merely because some books, treating these 
problems somewhat superficially, actually give figures 
like this as an example of how nervous connections are 
constructed. Let us agree that any straight line which 
has no cross-connecting point between its ends, shall 
always represent a standard length, and also, unless any- 
thing is said expressly to the contrary, a unit of resistance 
Such lines as SlM bi which has a crook inserted between 
its straight ends, are included under this definition. This 
line is drawn so as to indicate that it is not in contact 
with SlMl; for this purpose the method of drawing 
which is generally used by electrical engineers to indicate 
crossed, but mutually insulated wiring, has been adopted. 
A glance at the Figure 12 shows that the conductor 

S'br^ ^nMb 




Sb Sa 



Mb 



Fig. 12 — Impossible manner of connection. 

S h S\M a M a connecting the non-corresponding points S b and 
M a has not a greater resistance than the conductor 
S b SlMlM b , since both are made up of three standard 
lengths, although our requirement is that it shall have a 
greater resistance. We must look for a different kind of 
graphic representation to suit our needs. 

Neurology, that is, the anatomy and physiology of the 
nervous system as it actually exists and functions in 
animals and in man, teaches us an important fact which 
we ought to represent in any diagram of nervous connec- 



40 



HUMAN BEHAVIOR 



tions. It has been found that the same two points (one 
sensory and one motor) are almost generally connected 
in several ways, by shorter and also by longer conductors. 
For example, if pain is caused in a dog's foot and the foot 
is withdrawn, the nervous excitation may travel from the 
foot to the spinal cord and thence to the muscles moving 
the foot. Or, it may travel from the spinal cord farther 
on to the dog's brain, thence back to the spinal cord and 
now only to the muscles. If we combine this require- 
ment of a two- (or many-) fold connection of greater and 
lesser length between corresponding points with our 
previous requirement that the connections of non-cor- 
responding points shall be longer than the (direct) con- 
nections of corresponding points, the diagram of Figure 
13 readily suggests itself. We draw four conducting 

C 




Fig. 13 — Imperfect manner of connection. 

strings from 8*, *S&, M\, and M\ and unite them in a 
central point which we may call C. AH our requirements 
are then fulfilled. We can travel from S a to the corres- 
ponding point \l a over a longer route by C (four stand- 
ard lengths), or over a shorter route (three standard 
lengths) avoiding C; and we can travel from S a to the 
non-corresponding point M b only over a longer route 



IMPROVED MANNER OF CONNECTION 41 

S a SlCMlM b of four standard lengths. The same holds 
good for starting from the sensory point S b . 

Nevertheless, this diagram of Figure 13 is not yet 
quite satisfactory, but must be perfected in at least two 
ways. First, an excitation starting from one sensory 
point, for example S a in Figure 13, can hot only pass, over 
various routes, as we have seen, into the conductors 
M\M a and M\M h , but also from C into the conductor CSl 
and from Ml into the conductor MlSl, and then further 
from Si into the conductor SlS b . Thus the excitation, 
whose ultimate end is naturally the causation of contrac- 
tion in contractile tissues, would be only partly used for 
this end; a large part would be wasted by going into 
sensory points where, in animals with highly differentiated 
tissues, no contraction is possible. We must, therefore, 
draw our diagram in such a manner that the passing of any 
excitation into a sensory point is excluded. One way of 
doing this is by drawing each conductor, each neuron, in 
the shape of an arrow-like rod as shown in Figure 14. We 



A> 




Fig. 14 — One-way valves. 

can then easily agree and remember that the point of any 
arrow shall mean that no excitation can enter here from 
aay other neuron whereas the split end shall mean that 
an excitation can enter here, but can not pass out. Any 
point like the point D in Figure 14, where several neurons 



42 HUMAN BEHAVIOR 

meet, indicates then, according to the manner of drawing, 
that an excitation may pass from AD into either DB or 
DC, l)iit that no excitation can pass from either CD or 
BD into DA. It is as if a double one-way valve located 
at I) allowed the How of a fluid in one direction, but pre- 
vented the flow in the opposite direction. We must ask, 
of course, if the facts known to neurology permit the 
assumption that the meeting point of two or more neurons 
functions like a one-way valve. 

Experiments have proved, it is true, that an excitation 
may travel to the other end of a neuron, in whatever end 
it is called into existence by the application of an artificial 
stimulus. But with respect to the propagation from 
neuron to neuron, neurological experiment and observa- 
tion seem to agree with the view expressed in the diagram 
of Figure 14. Everybody knows that our feet are con- 
nected with our eyes as well as with our ears, and, of 
course, also with other sense organs. If a strange and 
ferocious looking animal suddenly appears to any ordinary 
person's eye while he is sitting, he jumps up and starts 
running. If he is sitting in the theater, and suddenly 
the fearful cry "fire" strikes his ear, he also jumps up and 
starts running. That is, the muscles moving his feet are 
connected with his eye as well as with his ear. But his 
eye and ear are connected with many other muscles too; 
else, for example, he would not turn his head in response 
to a friend's call or eat what is placed before him on the 
dinner table. Xow, neurologists have discovered in the 
brain the so-called motor region of the foot. If this 
region of the brain is artificially stimulated, the muscles 
belonging to the foot contract and move the foot. Sup- 
pose the excitation caused by the stimulus could proceed, 
not only in the direct ion of the motor organs most closely 
connected, but also in the direction of sense organs, for 



ONE-WAY VALVES 43 

example, the eye and ear. The eye and the ear are 
very closely connected with the motor region of the foot 
in the brain; they are also very closely connected with 
many other muscles of the body. It should then have 
been observed that in response to the artificial stimulation 
mentioned not only the foot, but many parts of the body 
moved. If such were the case, the neurologists would 
never have discovered the motor region of the foot. This 
very discovery means that they observed an exclusive 
reaction of the foot to stimulation of this region of the 
brain. We are justified, then, in our assumption of a 
one-way propagation of an excitation from neuron to 
neuron. We need not assert, dogmatically, that no other 
interpretation of the experimental facts is possible. But 
the assumption of one-way conduction from neuron to 
neuron, always away from sensory points and toward motor 
points, is simple enough and does not contradict any 
known facts. Besides, the anatomical connection be- 
tween neurons is of such a wonderfully elaborate kind, 
that it seems quite probable that the meeting points have 
a peculiar function, actually perhaps much more compli- 
cated than the simple function of a one-way valve. The 
neurons do not run into each other like wires soldered 
together, but their end branches are interwoven. The 
purpose of this method of connection is not known, but 
it surely involves more than a mere making one out of 
two. 

We said above, with reference to Figure 13, that the 
diagram of that figure needs additional features in order 
to make it more perfect. First, then, we shall draw the 
meeting point of several neurons in the manner of Figure 
14, indicating for each neuron the direction from a sensory 
point and the direction towards a motor point. A second 
improvement is necessary because the diagram of Figure 



44 HUMAN BEHAVIOR 

13 does not permit the representation of a series of motor 
points which can all be reached from one definite sensory 
point, but only over conductors each differing in resistance 
from all others. These conductors, in order to have each 
its special resistance, must all differ in length. At the 
same time, each motor point may have its own sensory 
point with which it is connected by a conductor of mini- 
mum length. The whole case, then, is somewhat com- 
parable to that of the jelly-fish in Figure 11, where all 
contracting points can be reached from any point stimu- 
lated, but only over paths differing in resistance. The 
insufficiency of the diagram of Figure 13 becomes clear 
if we enlarge it by connecting (in Figure 15) in the same 
way not only two, but three pairs of corresponding points. 
In Figure 15 an excitation can travel from S a to M a over a 
path of three standard lengths. From S a to M b an 
excitation can travel only by C over a path of four standard 
lengths. We have, therefore, a difference of resistance. 
But from S a to M c there is again a path of four lengths, 
so that there is no difference of resistance between the 
path leading to M b and that leading to M c . In order to 
represent a gradation of resistances we need a diagram 
differing from that of Figure 15. Instead of a point C, we 
have to introduce a line, as shown in the horizontal lines 
of Figure 16, representing each a neuron of standard 
length and resistance. In other words, the connections 
between the arches must themselves be arches consisting 
of three (or more) neurons each. 

In Figure 16 three colors have been used in order to 
facilitate the recognition of the direction from sensory 
points to motor points. All green conductors in the 
figure can be traveled only in the direction from below 
up, all red ones only in the direction from above down, all 
violet ones only in the direction from the left to the right. 

We can travel, in Figure 16, from S a to M a over S\ and 




<co .-3 



0) 



.2 

O 

o 



I 



g 



ARCHES OVER ARCHES 



45 



M I directly, taking a path of three lengths. From S a to 
M b the shortest path is over Si, S^,, M 2 ab , and M\. 
This path has a total length of five units, two more than 
from S a to M a . 

From *S a to M c the shortest path is over Si, fi^, Sl bc> 
Mlba M 2 bc , M\. This path has a total length of seven 



1 aba 

units 



At the same time the corresponding points S b and 
C 




S c S b S a M a M b M c 

Fig. 15 — Imperfect manner of connection. 

M b are connected by a short path (S b , Sj, Ml, M b ) of 
three units, the corresponding points S c and M c also by a 
short path (S C9 Sj, M\, M c ) of three units. This dia- 
gram, therefore, exactly fulfils the condition of universal 
connection without interference with local responsiveness 
of an animal's body. We shall have to investigate 
whether a nervous system like the one represented in 
Figure 16 is sufficient for the needs of all the higher and 
the very highest animals, — whether we have a right to 
assume that even the nervous system of man is built 
essentially (apart from simplification and elaboration of 
the details) on the design of this figure. We have, of 
course, the right to assume this, if wfc can convince our- 
selves that all the actual functions of the nervous system 
in man's body are thus made comprehensible. 






FOURTH LECTURE. 

Reflex arehes. Their peripheral and central points. 
Central sensory points and central motor points. Central 
points of a lower and higher order. Lettering of diagrams 
explained. Central sensory and central motor neurons. 
Reflex and instinct. Instinct a selecting and collecting agent. 
Overflow of a strong sensori-moi or discharge intothe most closely 
connected arches. The source of motor power different 
from the signal for its expenditure. What a nervous excita- 
tion can be likened to. Signaling by rods and levers or by 
pneumatic tubes. Velocity of signal very great, but not infi- 
nite; not dependent on intensity. A neuron likened to an 
electric storage element. A simple picture of a nervous 
process needed for our imagination of nervous function. 

THE design of Figure 16 allows infinitely many 
modifications and elaborations without deviat- 
ing from the general principle upon which it 
is based. This principle may be stated in the 
following words. Each sensory and each motor point 
of the body contains one of the ends of a neuron which, 
accordingly, may be called either a sensory neuron or a 
motor neuron. The other ends of each pair of a sensory 
and a motor neuron are connected by what may be called 
a connecting neuron. The whole, represented in the figure 
in the shape of an arch, for example, S a Si M\ M a9 may 
be called a reflex arch. Each reflex arch is composed of 
at least one sensory, one motor, and one connecting neuron. 

46 






REFLEX 47 

The number of neurons, however, forming a reflex arch, 
need not be limited. Any T ine in our diagram, the sensory 
neuron S a Sl, for example, might actually be a chain 
composed of several neurons. But for our present purpose 
of constructing a simple diagram typical of the design 
of the nervous system, this possibility need not be dwelt 
upon. Further, several sensory neurons may run to- 
gether into a ccmmon meeting point, as S d Sl, S d Sl, 
and S' d S d in Figure 17. And the same may be true for 
several motor neurons, as M\M b and M\M b in the same 
figure. Nevertheless we may say, since to generalize 
is our present business, that each reflex arch is composed of 
a sensory, a connecting, and a motor neuron. We must 
say a word, however, as to why we have called these arches 
reflex arches. The term reflex has been a physiological 
term for centuries. The early physiologists used it to 
signify the great quickness and definiteness with which 
certain actions occur compared with the slowness and 
variability of others. To take an example from human 
life, if we bring the tip of the finger suddenly close to the 
eye of a stranger sitting opposite us in the street car, he 
surely and most quickly shuts his eye. Such an action 
seems to deserve the name of reflex action. It occurs, 
or seems to occur, as promptly and definitely as our own 
features are reflected back towards us when we look at 
ourselves in a mirror. But if we ask the stranger to lend 
us a dollar, he puts his hand in his pocket — if he does it 
at all — only after a good deal of hesitation, of delay. 
This does not seem to deserve the name of reflex action. 
Modern physiology, however, has gradually put less 
and less emphasis on the quickness of the response 
in the case of so-called reflexes, and more on its definite- 
ness. For example, in such reflexes as coughing, or vom- 
iting, or intestinal action there is not necessarily any great 



48 HUMAN BEHAVIOR 

quickness, but a great definiteness of response. Now, we 
may most naturally regard the definiteness as being deter- 
mined by the fact that of the innumerable motor outlets 
of the excitation just one is superior to all others in being 
reached over the shortest path, offering the least resis- 
tance. Such a path may be represented by one of the 
a relies of our diagram, since each arch assigns to each sen- 
sory point just one motor outlet of specially low resistance. 
We may, then, call these arches reflex arches, but we 
must remember that by giving them this name nothing 
is proved or disproved, nothing is made clearer than it 
would be otherwise, — we have merely referred to a tra- 
ditional physiological term when occasion seemed to offer. 
Each reflex arch contains four points. We may give 
them different names by calling them peripheral points 
(S a and M a , for example) and central points (Si and Ml, 
for example). These terms "peripheral" and "central" 
must not, however, be understood literally. The peri- 
pheral points are not always located on the anatomical 
periphery of the body, the skin; — some sensory points are 
located in the skin and some in the inner parts of the body, 
whereas the motor points, in muscle fibers, are neces- 
sarily without exception beneath the skin. Neither are 
the central points always located in a central part of 
the body. The words peripheral and central are used in 
a loose sense, as a telephone station in a city is called 
central, although it may be located far from the centre 
of the city. We may then speak, not only of a peripheral 
sensory point and a peripheral motor point, but also of a 
central sensory point (S l a ) and a central motor point (Ml). 
This does not signify that these points are in a strict 
sense sensory and motor, but merely that one of them ($1) 
is nearer to a sensory than to a motor point of the body, 
and the othe~ (Ml) is nearer to a motor than to a sensory 



CENTRAL POINTS 49 

point of the body. It is easily seen, then, that in the dia- 
grams of our figures several central sensory points are 
collected, so to speak, by neurons (central sensory neurons) 
into a central sensory point of a higher order. For exam- 
ple, S\ and Si are collected into S% b . This is done in 
a manner not different from that in which the peripheral 
sensory points S b and S b are collected into S b . The 
central motor points are also collected (by central motor 
neurons) into central motor points of a higher order, 
for example, Ml and Ml into M 2 ah . The same prin- 
ciple of design is then applied again. From the cen- 
tral sensory point to the central motor point of the second 
order there are several paths — a direct one (S 2 ab M 2 ab ) 
and more indirect ones, for example S 2 ab Sl bc M\ bc M 2 ab . 
We find there the same manner of connection 
which we found for S l a and M*, which too had a direct 
and a less direct path of communication. The whole 
design, complicated as it looks at first, is really built 
upon a very simple principle, applied consecutively in 
regular order, — the principle, that from a sensory to 
its corresponding motor point there are always direct 
and less direct paths of communication, and that the less 
direct paths serve the purpose of connecting each sensory- 
motor system of conductors with other systems of a similar 
kind by the aid of a common path, always represented 
graphically by a horizontal line. 

The letters and digits added below or above each 
S or M very simply indicate the peripheral points with 
which the point in question is most directly connected 
ffor example, Sf cd with S b , *S&, S c , S d , S' d9 and S d ) and the 
total number of unit conductors making up any such 
connection (for example, three neurons for S bcd , two 
tor S^). Where the number of units differs for differ- 
ent peripheral points, the digit is added, not to S or M 



50 IHMAX BEHAVIOR 

hut to a, /;, c\ etc., as the case demands. For example, 
in the diagram of Figure 17, S fl W indicates that the dish 
tance from this point to S a is one of only two unit lengths, 
hut to S b of three lengths, and to S c also of three lengths. 

We spoke of the physiological term reflex. We may 
use this opportunity to refer now to another traditional 
term, that of instinct. When one observes that a bird, 
without having been taught by experience or by other 
birds, builds a nest before laying any eggs, one usually 
says that the bird has done this instinctively. Here again 
there is a certain promptness and definiteness of action as 
in the case of a reflex action, but promptness and definite- 
ness of a different kind. Let us try to make clear of what 
kind. The bird does not many times lay eggs which are 
doomed to perish because there is no place to receive 
them, until some time it happens to prepare a nest before 
the act of laying. But before the first egg is laid, the nest is 
prepared in quite a definite way, well suited for the 
hatching of the young. Of course, there are certain 
physiological processes in the bird's body which, previous 
to laying, cause excitations in definite sensory neurons, 
and these excitations are conducted to the motor neu- 
rons controlling the act of building. Why are they con- 
ducted just here and not to any other motor neurons? 
Obviously, because of short connections, of relatively small 
resistance, between these motor and these sensory neurons. 
But the figure of speech of a "mirror-like reflection" is not 
applicable. We cannot comprehend an instinctive 
activity by simply referring to a reflex arch, — it is too 
complex and variable for that. It is definite only in the 
sense that it occurs at a time when innumerable stimuli 
acting on innumerable reflex arches make us regard almost 
any other kind of muscular activity as just as probable as 
the one which actually occurs, some of them stimuli 



INSTINCT 51 

without the presence of which the act of building w T ould 
not have occurred, some, however, quite irrelevant to the 
act of building. For example, a suitable site for the nest 
and suitable building material must impress themselves 
upon the eyes. But even this site and this material 
might have called out innumerable other responses just 
as well. The specific excitation of the instinct, caused by 
the internal physiological stimulus aforementioned, there- 
fore cannot be the all-sufficient cause of the action, but 
must be rather of the nature of a selecting and collecting 
agent, weakening and rejecting those excitations whose 
presence is unnecessary, or whose reflex responses would 
interfere with the instinctive action, strengthening and 
uniting all those excitations whose presence is necessary 
for the performance of the instinctive action. Let us 
now try to comprehend the effect of the specific excitation 
of the instinct by the application of the diagram of 
Figure 17. 

Let S d S\ represent all those sensory neurons any exci- 
tation of which is likely to interfere, if the corresponding 
reflex responses are allowed, with the performance of 
the instinctive activity. To illustrate this by a concrete 
example, think of flying. It is clear that any long continued 
flight would make nest building an impossibility, even 
though short flights are with many birds an essential 
part of the building activity. Here a selection is needed, 
excluding, on the whole, such motor responses as flight. 
Let, further, S b S\ and S c S] represent all those sensory 
neurons whose excitation is necessary for the instinctive 
activity. For example, the bird's eyes must see the 
site and the material. Here a collection is needed, including 
in the activity the 4 motor responses^ upon such things 
as a building site and building material. Let S a S\ repre- 
sent the sensory neuron whose excitation is what we 



HUMAN BEHAVIOR 

called the specific excitation of the instinct, which selects 
and collects among the nervous processes coming from the 
other sensory points. How, then, can we comprehend 
the influence of the excitation coming from S a upon the 
motor activities at the points M b , M C9 and M d ? Obviously, 
the excitation coming from S d must be prevented from 
reaching the corresponding motor point M d . The excita- 
tions coming from S b and from S c , however, must not be 
prevented from reaching their corresponding motor points 
M b and M c , but their effectiveness must be enhanced as 
much as possible: — the bird must not do any other 
things, but pick up building material and drop it at the 
site of the nest in the proper manner leading to the forma- 
tion of a nest. 

It seems clear that this acting as a selecting and collecting 
agent as we said above, can be best understood by assum- 
ing that the excitation coming from S a9 being so strong 
that the direct discharge over S* and Ml into M a overflows 
the channel of its reflex arch, partly travels upwards from 
the point S\. Because of the connections naturally 
existing it can reach equally well both Ml and M\ 
over shorter paths than it could reach any other points 
(e. g., M\ ) leading towards motor organs. Thus it en- 
hances the muscular contractions at both the motor points 
M b and M c . The connections of the generalized design 
of Figure 16, however, do not fulfil this condition. They 
would favor M b over M c . The connections representing 
the instinct must be like those of Figure 17, which is 
derived from Figure 16, in the main by simply omitting 
certain conductors, as a comparison of the two figures 
immediately reveals. If we travel in Figure 17 from S a 
to any motor point other than M a over the shortest pos- 
sible route, we can travel only over S fl , S a 2 b s c s , and 
M a * b *c* to either M h or M b ov M c . In this case the entire 



A SELECTING AND COLLECTING AGENT 53 

path from the sensory to the motor points has a total 
length of six units. Had we traveled from S a VV U P to 
SaVcV an d A/aVcV an d thence to any other motor 
point, for example, to M d , the path would have had a total 
length of at least eight units. The control by the strong 
and overflowing excitation from S a of the function of the 
motor points M b and M c , the collecting agency of the in- 
stinct, is thus graphically represented by the relative 
shortness of the connecting conductors. On the other 
hand, the inhibiting influence of the excitation coming 
from S a upon the function of the reflex arch S d M d is 
graphically represented by the bare existence of a connection 
by means of the connecting neuron S a V c V M a s b 4 c 4 d 4 . 
This connection must make it possible for the nervous 
process coming from S a to capture, as it were, the nervous 
process coming from S d , thus preventing it from reach- 
ing M d . But we are still far from understanding this in- 
hibiting, selecting influence. The diagram of connection 
by conductors in Figure 17 is only one of the assumptions 
necessary for the explanation of instinctive activity. We 
shall return to this problem in the following lecture. It is 
necessary that we investigate first what other assumptions 
we have to make to understand theoretically what nervous 
activity means. 

We have already compared the nervous system with a 
signal system, a telephone system by means of which 
messages may be sent. We must understand more clearly 
what kind of a signal system it is. It is important, how- 
ever, that we keep clearly before our mind that it is only a 
system for signaling, not a system for the transmission of 
power. It can not be compared, for example, with the elec- 
tric light and power circuit of a city, furnishing to many 
houses in many streets power which is generated in a cen- 
tral station. An animal's muscular power does not take 



54 



HUMAN BEHAVIOR 



its source in the nervous conductors attached to the mus- 
cles. The power is derived from the digested food through 
mediation of the blood circulation. The power is thus 
stored in the muscles, ready to be expended at the proper 
signal. The nervous excitation is the signal, the message 
that the power should be expended. To be sure, the 
amount of power expended is not altogether independent 
of the force of the signal, of the intensity of the mes- 
sage received. But that the power is not derived from 
the messenger is clear from the fact that when a muscle is 
exhausted, no nervous excitation can make it contract. 

What, then, is the excitation which is propagated 
through a nervous conductor in order to serve as a signal 
to a muscle fiber. This, however, is not really a good ques- 
tion. What it is, in other words, what name is to be 
applied to it, is directly of little significance. What it 
can be likened to, is the question which we should rather 
ask. What thing with which we are familiar in the ordi- 
nary functions of life, acts like a nervous conductor through 
which an excitation is taking its path? 

Fifty years ago, when a master desired to call his servant, 
he rang the bell in the servant's room by means of a rigid 
wire connection extending over pivoted angles from his 
own to the other room. Now, let nobody think that this 
comparison is absurd from the start. Everybody knows, 
of course, that there are no wires and pivots in any nervous 
system. But we have already emphasized that it is 
of minor importance what there is, that we are concerned 
rather with what goes on there. Does the signaling 
going on in the nervous system permit comparison with 
the signaling done by pulling a bell cord? Now, it does not. 
If for no other reason, for this, that the bell attached to 
a perfectly rigid wire or rod begins to ring the very 
moment the other end is pulled. But when an excitation is 



ANALOGIES OF CONDUCTION 55 

caused at one end of a nervous conductor, it is not at the 
same moment also at the other end, but measurably la- 
ter, — the later, the greater the distance between the 
two points. We must look, therefore, for a different com- 
parison. 

Everybody knows the grand musical instrument in 
which the player, pressing down the keys, opens at consi- 
derable distances from the keyboard the valves which 
make the various sources of sound speak. In the pipe or- 
gan too the messages were sent until comparatively recent 
times from the keys to the valves by means of rigid connec- 
tions, as from the master's room to the bell in the ser- 
vant's room. No delay is permissible in the response of 
the pipes to the touch of the ringers on the keys. The 
rigid connection, therefore, seemed to be the only possible 
one. Nevertheless, the modern organ has been freed of 
all rigid connections. A narrow tube runs from the key 
to the pipe valve. The motion of the key opens a tiny 
auxiliary valve which admits compressed air from the 
main reservoir to the tube just mentioned. At the 
other end of the tube is a tiny bellows which is raised 
by the compressed air and thus operates the pipe valve. 
Now, what use can we make of our knowledge of this 
familiar mechanism? We shall see at once that we can 
thus elucidate certain fundamental facts of the function 
of the nervous system. The pneumatic mechanism does 
not operate the pipe valve at the very moment when the 
key is moved by the finger, but at a measurably later 
time, — the later, the longer the connecting tube. How- 
ever, the time interval is short enough to be negligible 
in musical practise, provided the connecting tube is not 
extraordinarily long. The time interval is practically 
independent of the density of the compressed air in the 
reservoir. It is simply proportional to the length of the 



56 HUMANjBEHAVIOR 

tube, provided the tube is plain and does not contain in 
its course any additional mechanisms. The corresponding 
tacts are found in the function of the nervous system. The 
muscle fiber docs not contract at the very moment when 
the sensory point is excited, but some time later, — the 
later, the longer the nervous path connecting the sensory 
and the motor point. Yet, the time interval is, in the 
case of a reflex, quite negligible according to our standards 
of time in ordinary life, — so much so, that for centuries, 
until modern methods of measuring exceedingly short 
time intervals were invented, the time was regarded as 
absolutely zero, that is, the response was indeed believed 
to occur at the very moment when the sensory point was 
excited. It has further been shown by experiment, 
that the contracting of the muscle fiber does not occur 
any sooner if the excitation of the sensory point is made 
stronger. 

With all this, however, we do not want to suggest 
that a neuron is a narrow tube through which a fluid is 
pressed. We have emphasized before that we are merely 
searching for familiar functions with which we may com- 
pare the nervous functions in order to assist our power 
of imagination and reflection. Let us use this opportunity 
to tell briefly what physical processes have actually been 
found by the neurologists to go on in the nervous conduc- 
tors. Whenever anything of the nature of an excitation 
occurs in a neuron, an electrical phenomenon is observed. 
Hut it is generally admitted that this electrical phe- 
nomenon is not the excitation itself. There is no such 
thing as an electrical insulation surrounding a neuron, 
which would enable an electrical current to pass along 
a neuron. And further, the velocity with which the exci- 
tation is conducted is almost infinitely small when com- 
pared with the velocity of electricity in its conductor. 



STREAMING OF IONS 57 

During the time a nervous excitation is conducted one way 
and back through an elephant or other large animal, elec- 
tricity can circle the globe. The electrical phenomenon 
must be, therefore, a purely accidental accompaniment of 
the conduction of an excitation. It is highly probable that 
the conduction of the excitation is a process of a chemical 
nature. The substance of a neuron, consisting of highly 
unstable organic compounds, must be well adapted to 
the conduction of chemical changes. It is also well known 
that the conduction of chemical changes frequently 
involves, as by-products, so to speak, electrical phenomena. 
Indeed these electrical phenomena accompanying the 
conduction of chemical changes have been used technically 
and have become of the greatest industrial importance 
in the so-called accumulators or electrical storage batteries. 
An accumulator is essentially a conducting fluid on the 
sides of which there are two related, yet different chemical 
substances, most commonly lead compounds. One of 
these substances has a tendency to take up a certain 
more elementary substance; the other has a tendency 
to give off this same elementary substance. The same 
elementary substance is one of the components of the con- 
ducting fluid. What happens is this : A stream of element- 
ary substance flows — or, whatever it may actually do, is 
imagined to flow — from one end of the conductor to the 
other, and this flow, the wandering of molecules or ions, 
as it is usually called, is accompanied by an electrical 
phenomenon. We are, then, probably justified in regard- 
ing the conduction of an excitation through a neuron as, 
not identical with, but at least analogous to the wandering 
of ions through the conducting fluid — the electrolyte, 
to use the technical term — of a storage battery. 

Concerning the chemical and physical properties 
of the neurons hardly anything further is known which 



58 III MAX BEHAVIOR 

could make the function of these wonderful structures 
clearer. It is not especially remarkable that the chemistry 
of the neuron, although it has attracted in recent years 
the attention of investigators, has made little progress. 
We need only remember that the neuron is a microscopic 
structure, and that for a chemical analysis a more than 
microscopic quantity of the substance to be analyzed is 
required, and we understand why no one yet knows how 
the excitation actually wanders from one end of a neuron 
to the other end and thence to the other neurons. For the 
very reason that the chemistry of the neurons is a thing 
of the future, we may picture to our own imagination 
the processes going on in the neurons in terms not neces- 
sarily chemical, in any kind of terms with which we are 
familiar and which enable us to understand the function 
of the nervous system as being a complex of a few — as 
few as possible — simple functions. We have pictured 
it as a process like the one going on in a connecting tube 
of a pneumatic organ. Let us now draw further conclu- 
sions from this assumption. 



FIFTH LECTURE 

Advantage of comparing the nervous process with a pro- 
cess of streaming. Analogy of the jet-pump. The whole 
nervous system permeated by any nervous process, but not 
with uniform intensity. Suction at motor points; openings 
made at sensory points. Velocity of the relief of tension. 
Conditions of the intensity of streaming at any definite 
point of the system. Exhaustion. Resistance increasing 
with, and even more rapidly than, the flux. Overflow not 
identical with universal permeation. The selective function 
of an instinct explained by the principle of deflection, the 
collective by that of overflow. 

SPEAKING of the fundamental facts to which one 
customarily refers by the term instinct, we showed 
(page 53 and Figure 17) that one of them consists 
in the capturing of the nervous process going on 
in one reflex arch (S d M d ) by the nervous process going on 
in another reflex arch (S a M a ), in such a manner that the 
former process, coming from S d , could not reach its normal 
end in the motor point M d . Does it help us to understand 
this possibility of one nervous process capturing another, 
deflecting it from its normal course, if we compare nervous 
processes with the conducting mechanism of a pneumatic 
organ? It does indeed, although no such capturing takes 
place in an organ. The little bellows operating a pipe 
valve is filled by air streaming through the connecting 
tube. Now, it is one of the most interesting facts of 

59 



60 HUMAN HKIIAVIOR 

physics that a stream can defied (mother stream with which 
it is in contact. This is equally true for gaseous and 
liquid substances, there being in this respect no funda- 
mental difference between them. We are all familiar 
with many kinds of apparatus using this principle of 
deflection. Think of the various sprayers for spraying 
perfumes or substances for inhalation, or for spraying 
with insecticides the vegetables growing in the fields. 
In these sprayers the liquid to be distributed is usually 
taken — deflected,* if we wish to say so — from the vessel 
in which it is contained, by a stream of air. Or think of 
the jet-pump, draining, perhaps, the cellar under our 
house, or exhausting air from a glass bell in our laboratory. 
It is not necessary for us here to discuss these phenomena 
from the standpoint of theoretical physics, to explain 
them mathematically. It is sufficient to mention them 
as familiar facts. In all these cases it is irrelevant, of 
course, whether the deflected stream really streams 
originally with a positive or a negative velocity or 
happens to have a zero velocity, that is, happens to 
stand still, as in most of the examples mentioned above. 
We can speak of deflection in every case. 

Now, if the wandering of an excitation through a neuron 
is comparable to the streaming of a fluid, we understand 
at once the possibility of the deflection of one nervous 
process by another. This deflection of a nervous process 
from its ordinary course is then no longer a strange pheno- 
menon, but has become like an old acquaintance. We 
no longer ask any curious questions about it. We might, 
possibly, inquire after the physiological details of this 
function of the contact point or points of the two nervous 
path-, where the deflection is brought about. But our 
curiosity in this respect is not very great as long as we do 
not even know the kind of chemical changes which are 
conducted through the neuron. 



ANALOGY OF THE JET-PUMP 61 

We have spoken of a chain of neurons as if it were a 
tube through which air (or any fluid) is pressed from a 
reservoir containing air under higher pressure. There 
are, however, some disadvantages in picturing a nervous 
process in this way. There is actually nothing which 
resembles a reservoir from which any power or any sub- 
stance enters, by way of a sensory point, into a chain of 
neurons in order to be pushed along; and this pushing by 
pressure might suggest a wrong idea of the function of 
the nervous system. Some one might think that, what- 
ever it is that is pushed from a sensory to a motor point, 
it will take — like a rolling ball — only one way and entirely 
avoid all other possible ways. Thus, indeed, one finds 
nervous processes most commonly described in the older 
literature of neurology. The question would then have 
to be asked why such a process can take, now one, now 
another path, why it does not always take the same, 
since there is no god, no supernatural entity, in our ner- 
vous system to act as switchman, to sever the connections 
of the first path and to establish new paths, by voluntary 
action. This question is then unanswerable; the fact 
appears like a miracle. We must not think, therefore, 
of a nervous process as ever taking strictly a single path. 
We must, on the contrary, think of any nervous process 
as permeating the whole nervous system, but only along 
a certain path with great intensity, along all others with 
very small intensities. Only thus can we understand the 
function of the nervous system as a unitary function. It 
is, therefore, better not to think of the nervous process as 
something being pushed, but rather as a fluid filling the 
whole network of neurons and being attracted by, sucked 
in the direction of, all the motor points of the body. It 
is true, to those who are accustomed to imagine in mathe- 
matical terms movements of a liquid or a gas, there is no 



62 HUMAN BEHAVIOR 

essentia] difference between a stream of a fluid caused by 
pressure at one end and a stream caused by suction at the 
other. Hut those not accustomed to mathematical reflec- 
tions on such phenomena, will probably remember the 
all-permeating nature of any process in the nervous 
system more easily if they think of the cause of the stream- 
ing as something located in the totality of the motor 
points. 

Let ns, therefore, make the assumption, that the nervous 
system functions as if the neurons were tubes filled with a 
fluid, as if at all the motor points there were a constant 
suction tending to draw the fluid in the direction of each 
and every motor point, and as if an excitation of any 
sensory point were equivalent to a greater or smaller, 
but always minute, opening of the tube at this point, thus 
allowing a streaming motion of the fluid within the tube 
system. When a system of tubes like the diagram of 
Figure 16, with one-way valves at all the meeting points 
of tube-units, is closed at all those points which we have 
called sensory points, no streaming of the fluid is possible 
in any of the tubes, in spite of the suction at all the motor 
points. Another effect, however, results from the suction. 
The whole fluid in the tubes must assume a definite 
tension, whose force must become equal to that of the 
suction. Then the tension remains constant until a 
stimulus is applied to a sensory point, or, as we have said, 
until one of the tubes is slightly opened at a sensory point. 
One must not think that immediately when the opening 
occurs, the whole column of fluid begins to stream. What 
happens first, is a relief of the tension at the point where 
the opening is made. Then, as in every elastic substance, 
so in the fluid, the relief of tension passes on. Only when 
the relief of tension has reached the point where the force 
of suction is effective, that is, the motor point, can the 



RELIEF OF TENSION 63 

actual streaming begin. The velocity with which the 
relief of tension travels through the fluid, is exactly what 
is ordinarily called the velocity of sound in an elastic 
substance. In a neuron we have to call it the velocity 
of the nervous process, — whatever the nature of that process 
may be. The velocity of the nervous process, which may 
be regarded as a constant numerical value, and the length 
of the conductor leading from the sensory to the motor 
point determine, therefore, the time which elapses between 
sensory excitation and the start of the motor response. 

The relief of tension, and the subsequent streaming, in a 
system like Figure 16, can take simultaneously many 
paths in the direction of a motor outlet. Which of all 
these paths is chiefly taken, is determined by the relative 
resistance of the conductors. We must not imagine, — 
as we have emphasized before and restate here in more 
detail — that the relief of tension rolls on like a ball, strik- 
ing an obstacle, rebounding, running into an open channel, 
and so on, finally reaching one motor point exclusively. 
The relief of tension travels to every motor point which 
is directly or ever so indirectly connected with the sensory 
point in question. That it reaches motor points of direct 
connection sooner than those of indirect connection, is 
clear; but this time difference does not especially concern 
us at present. The streaming, subsequent to the relief 
of tension, also occurs everywhere, — in every neuron 
which is a chain in any path from the sensory point to any 
motor point. But the intensity of the streaming, the 
flux at any definite point within the nervous system, is 
necessarily determined by the relative resistance of the 
total path over this point (not the resistance of any single 
point) from the sensory to the motor point and the resist- 
ances of all the other paths leading from the same sensory 
point to all the motor points. To get a more definite 



64 



HUMAN BEHAVIOR 



image ot such a complicated phenomenon, lot us think 
of two incandescent electric lamps illuminating our room, 
which in the ordinary manner are placed parallel into the 
circuit. Suppose the wiring provides for two twenty 
candle-power lamps, but we suddenly replace one of them 
by a c 2()0 candle-power lamp of correspondingly less 
resistance. Immediately w r e see a diminution of the 
brightness of the other lamp, because its higher resistance 
keeps the current from passing through it in its normal 
strength. Now imagine that in Figure 18, which is 









) 1 I \ ^ 


Sd 


) J 


rM'c 




s 






Sd' 


( > I 


■Hi 






, / 


k 







Sa Sd S c Sd M d (1 c f1 b M a S e Sf S g M g M f M e 
Fig. 18 — Possible modification of details in nervous architecture. 



merely a modification of Figure 16 on the same structural 
principles, each neuron w r ould be replaced by a thirty 
volt lamp and that then the point S a would be placed in 
contact with the positive line, and all the M points in 
contact with the negative line of a hundred and ten volt 
electric circuit. It is clear that the three lamps of the 
reflex arch S a M a would then glow visibly, but that the 
other lamps of the system would hardly glow at all, 
although a weak current must pass through them. Simi- 



PERMEATION OF THE SYSTEM 65 

larly, the muscular activity in the animal body becomes 
conspicuous only in the corresponding motor point, al- 
though a weak streaming must occur in the direction of 
every motor point in any way connected with the sensory 
point where the excitation starts. 

If we thus picture the nervous process as a streaming of 
a fluid in a system of tubes, made possible by an opening 
at one of the sensory points, we must, of course, imagine 
this opening to be, even when at a maximum, very small 
relative to the volume of a tube unit. Otherwise the 
tube, or even the whole system, would quickly become 
empty, exhausted. The nervous system, however, is by 
no means quickly exhausted, but can be active for many 
hours before taking a complete, or nearly complete, rest 
during the period of sleep. The opening at a sensory 
point being exceedingly small, the streaming of the fluid 
must be very weak. This does not matter, since the flux 
in various neurons is significant only through its relative, 
not its absolute magnitude. 

Two fundamental facts, with reference to the so-called 
instinctive activities of animal organisms, were to be 
explained : the deflection of one nervous process by another, 
and the simultaneous enhancement of the activity of 
several motor points. We have found that the former 
becomes comprehensible if we regard any nervous process 
as possessing the properties of a streaming fluid, provided 
the meeting points of the neurons, about whose functional 
properties we possess no actual knowledge whatsoever, 
are assumed to function in a manner comparable to the 
functioning of the simple mechanical device which is 
called a "jet pump." The simultaneous enhancement of 
the activity of several motor points can be satisfactorily 
explained as we have explained it in the preceding lecture, 
simply by an overflow and the inherited peculiarity of 



66 HUMAN BEHAVIOR 

aervous connections. If the excitation starting from S a 
in Figure 17 is not in the ordinary way practically confined 
to the reflex arch S a M a , but exceeds the capacity of the 
reflex arch and overflows, it will reach on a higher level 
the connecting neuron S a YV M a 2 b 3 c * an d hence pass down 
over the central point M\ c to both the motor points M b 
(and also M b ) and M c . Since the overflow finds an outlet 
from the level of S fl VV down, it does not reach the higher 
level of aSVVcV- This is important, for, if the overflow 
from S a reached this level, the excitation starting from 
S a would enhance the activity of the motor points M d and 
M d , instead of decreasing it by deflection, in accordance 
with our previous assumption concerning the significance 
of M b , M c , and M d in the instinct under discussion. The 
deflection of the nervous process S d M d , however, can be 
insured by a sufficient difference in level between the 
connecting neurons which in Figure 17 are represented 
by 8/ftV M a \\* and by S fl V,V M a \\\\ This differ- 
ence in level, of course, is not limited to what it appears to be 
in the simplified diagram of Figure 17. Only one question 
is thus left, namely, how we can speak of an overflow of a 
reflex arch (S a M a ) upwards, caused by the intensity of the 
excitation (at S a ), with the result that the activity of 
certain other motor points (M b and M c ) is not, as would 
be expected from the principle of deflection, weakened by 
the strong nervous process (from S a ), but on the contrary 
enhanced. This is a question of so much importance that 
we cannot proceed without having answered it with 
perfect clearness. It is particularly important to make 
clear the difference between an overflow and the fact that 
in the case of every nervous process very weak currents 
always go over innumerable paths other than the main 
path of the process. 

It is obviously not sufficient to state simply that the 
stronger nervous process deflects all weaker ones. There 



OVERFLOW 67 

arc exceptions to this rule, as in the present case. Every 
case in which, because of a very great excitation at a 
sensory point, the motor response is not practically 
restricted to the corresponding motor point, but becomes 
positively apparent also at other motor points, is an ex- 
ception to the principle of deflection. The stronger 
process, instead of canceling the motor effects at all motor 
points other than its own, while it may cancel many of 
them, enhances at least some of them, indeed may bring 
about some motor effects at points whose corresponding 
sensory points are not receiving any stimulation at all. 
Now, this can be understood only by assuming that there 
is an absolute limit to the flux in any neuron, or, — what 
amounts practically to the same and agrees better w T ith 
our previous assumptions, — that the resistance of any 
neuron is not independent of the flux within it, but in- 
creases more and more rapidly as the flux increases. We 
are familiar with a similar phenomenon in electric con- 
ductivity. As the current increases, the conductor gets 
hot; and in the case of most substances its resistance 
becomes the greater, the greater the temperature. Let 
us imagine that there is a similar, only much more rapid, 
increase of the resistance w T ith the increase of the flux in a 
conductor, and our problem is solved. If, under this 
condition, the excitation at S a in Figure 17 reaches a 
sufficiently great height, the intensity of the flux in the 
motor neuron M l a M a reaches practically an absolute 
maximum, and the overflow, which thus becomes inevit- 
able, must seek the motor outlet which offers the least 

i-tance because of the least length. This is in the 

< Dt case the outlet over »S a Vc 8 M a z h * c * M% c into M b , 

M , and M c . Of course, there can be, then, no question 

of any deflection of an independent nervous process in 

M. x or S M . Whether there is any such nervous 



(is IHMAX BKIIAVIOR 

process or not, the overflow from S a into M b and M c would 
occur anyway. At the same time, however, the nervous 
process S h }[ th if $ d happens to be simultaneously stimu- 
lated, is deflected into M b and M c , provided the overflow 
from S a has not reached the level of S a 8 6 4 c 4 ^ 4 ikf a WV- 
Overflow and deflection, therefore, are not fundamental 
principles which logically exclude each other. Their 
conditions merely enter now and then into a conflict, a 
state of affairs which is found in all natural laws. Let 
us keep in mind, then, that we do not mean by overflow — 
as someone might conclude who has not read our present 
discussion carefully — the fact that any nervous process 
permeates, although for the most part exceedingly weakly, 
the whole nervous system, far beyond the limits of a narrow 
path: — we mean an overflow caused exclusively by an 
intensity of flux taxing the capacity of a nervous path to 
its limit. 

We have called an instinct a selective and collective 
agency in the functioning of the nervous system. It is 
clear that the principle of deflection explains the selective, 
the principle of overflow the collective part of the function 
of an instinct, provided the inherited connections of 
sensory and motor points are such as represented dia- 
grammatically in Figure 17. 



SIXTH LECTURE 

Tension of the total muscular system not interfering with 
special activities. The motor point not identical with the 
point that is moved. Fewer reflexes, more instincts in higher 
animals. The compounding of nervous elements into groups, 
of these groups into larger groups, and so on, into a single 
nervous system. The nervous system of a worm. Nerve 
centers. Lower and higher centers. The nervous system of a 
crayfish. The brains of fish, frog, bird, and mammal. The 
nervous system of man. The cerebral hemispheres of man. 

SINCE we have had occasion to mention again at 
the end of the last lecture the fact that every 
nervous process permeates, although for the most 
part very faintly, the whole nervous system and 
thus, in a manner, reaches every motor point, we may 
explain briefly, that this does not conflict with our obser- 
vations of actual animal behavior. A slight degree of 
tension of all our muscles in no way interferes with specific 
activities involving a few definite muscles. Indeed in 
practically all our normal activities we find that at least 
one group of muscles other than those which actually 
pull is quite noticeably under tension, namely the so-called 
antagonistic muscles. Raise your arm in order to take 
off your hat. It can be easily observed, and there is no 
doubt whatsoever, that during the upward movement of 
the arm not only those muscles are under tension which 
pull the arm towards the head, but also those which under 

69 



70 HUMAN BEHAVIOR 

other conditions might pull the arm towards the body. 
The latter muscles, if we put our fingers on them, do not 
feel relaxed, flabby, but somewhat stiff. Only, the former 
muscles feel stiffer, they are under greater tension, and 
the arm, therefore, follows the direction determined by 
them. Under these circumstances, a general but faint 
permeation of the whole nervous system by any nervous 
process, however definite the activity for whose sake this 
process exists, involves by no means a contradiction. 

Speaking of muscles, it may be well to make a remark 
here which will help to avoid possible misunderstandings 
later. When a nervous excitation causes a movement of a 
definite part of the body, for example, of the arm, the 
motor point of the nervous path is not necessarily located 
in that part of the body, in the arm. Indeed, if a move- 
ment of the arm as a whole is in question, the motor 
point (more correctly, of course, points) must be in the 
muscles located at the shoulder and the front or back of 
the chest. The muscles located in the arm can not move 
the whole arm, but only the lower arm. The muscles 
located in the lower arm can not move the lower arm, but 
only the hand and the fingers. These examples may 
suffice to call attention to the fact, which is self-evident, 
that in highly developed animals the motor point must 
not generally be looked for in that part of the body of 
whose activity the nervous process is said to be the signal. 

We have thus far spoken of the fundamental facts of 
behavior in higher animals under two headings, that of 
reflex and that of instinct. We call an animal the higher, 
the fewer simple reflexes it has — relatively — and the more 
instincts. Since this difference in the relative number 
of simple and compound reflexes, that is, of reflexes proper 
and instincts, depends, according to OUT previous exposi- 
tion-, on definite structural peculiarities of the nervous 



INSTINCTS IN HIGHER ANIMALS 



71 



system, it seems interesting and promising to compare 
lower and higher animals with regard to the structure of 
their nervous systems. It is not a priori necessary, but 
probable, that these structural differences become apparent 
to the eye of the anatomist and zoologist, and if they do, 
they permit the correctness of our previous expositions 
to be tested. 

As our lowest type may serve the nervous system of an 
earth worm. Figure 19 shows the arrangement of the 
more bulky masses of the nervous system, omitting the 
many fibers which are found scattered over the body and 
which obviously serve as sensory and motor neurons. 




Fig. 19 — The bulk of the nervous system of an earth worm. 

What we see in the figure represents, therefore, in the 
main, merely the bulk of those connecting neurons which 
are added to the sensory and motor neurons in order to 
complete the reflex arches, and of those which serve to 
establish connections among the reflex arches, in accord- 
ance with the principles which we have discussed. We 
have seen that the frequent necessity of a body acting as 
a whole, the necessity of local responsiveness as found in the 
reflexes, and the presence of selecting and collecting agents 



72 HUMAN BEHAVIOR 

called instincts, have as a consequence a structure of the 
nervous system like the diagrams of Figures 16, 17, and 
18. Let us, at present, remember especially Figure 18. 
We notice there a number of sensory and motor points. 
Some of the reflex arches are united by the connecting 
neuron S~ bcd Mj bcd . The significance of the formation 
of such a group is obviously, together with the insurance 
of local responsiveness for each reflex arch, a unification 
of the group of reflex arches for the purpose of co-opera- 
tion. It is clear that co-operating reflex arches, as a rule, 
belong to, and so far as possible are located in, the same 
part of the body. Any part of the body which deserves 
to be called a limb or an organ, say, one finger, needs 
unitary activity of the totality of its own reflex arches for 
the sake of its own protection if not for other ends. This 
part of the body, then, is as a whole subject to the principle 
of local responsiveness, but must also be able to co-operate 
with other organs, to form with them anatomically and 
functionally a larger organ. For example, our fingers 
are united in our hand, not only anatomically, but also 
functionally, that is, by their nervous connections, thus 
making the hand a larger organ. We know that it is 
easier to make a fist than to bend each finger separately. 
These considerations lead us to expect groups of reflex 
arches to be united as we see two such groups united in 
Figure 18, where the central sensory points S 2 bcd and 
S 2 fg and the central motor points M 2 bcd and M 2 efg are 
connected as if they were peripheral sensory and motor 
points. The larger organ which is only thus made "an 
organ," enabled to function as a unit in addition to 
possessing local responsiveness of its sub-divisions, must 
again, perhaps, be united with other organs. That is, 
the whole mass of nervous conductors, sensory or motor, 
must again be united with similar masses — we might just 



GROUP FORMATION 



73 



as well say, systems — into a larger "nervous system." 
Where this building reaches its final culmination, depends 
exclusively on the anatomical development, the anatomical 
complication, and, accordingly, the demands of the body 
for nervous conductors to suit its functional needs. A 
simple way of representing this compounding of sensory 
and motor elements into groups, of these groups into 
larger groups, of these into still larger groups, and so on, 
finally into a single large system, is shown in Figure 20. 




> 1 

A 



l A 



Y 



Fig. 20 — Low and high centers: group formation in the nervous system. 

That the total mass of all nervous conductors thus forms 
a single system, and not two or three or more mutually 
independent systems, follows from the necessity of each 
animal body being able to act as a whole. In the figure, 
each group is composed of only two members, for sim- 
plicity's sake. In the body each group must actually 
contain, of course, a very large number of elements, in 
accordance with the special anatomical and functional 
demands. This large and varying number is represented 
in the diagram almost throughout by two. The dotted 
lines of the figure will be explained a little later. 



74 HUMAN BEHAVIOR 

Lei us now make the application to the earth worm. 
Let us sec what kind of a picture we can expect the earth 
worm's nervous system to present to our eyes. Since 
the worm's body is long and narrow, we expect that suc- 
cessive pieces, from the front to the rear, should function 
in relative independence. To make this still clearer, let 
us remember how the worm moves forward. The ab- 
dominal side of the body possesses tiny bristles pointing 
backwards, so that the body does not easily slide backwards 
on the ground. If, then, a fraction of the body, at the 
front end, lengthens in the manner which everybody 
knows from observation, the front end must be pushed 
forward. Suppose now the first half of this front end, 
the head, so to speak, remains inactive on the ground, 
but the second half actively shortens, and an equally long 
piece directly behind actively lengthens. The effect 
must be that the elements of the piece directly behind 
the head are, more or less, pushed forward. If now the 
piece which has just lengthened, contracts lengthwise, 
and the directly following piece lengthens at the same 
time, while all the rest of the body remains inactive on 
the ground, the elements of the third piece are pushed 
forward, more* or less. When in the same way every 
successive piece has been moved forward, we can say that 
the worm as a whole has made a step forward. It is 
immediately clear that the nervous system of this animal 
must be so constructed that the successive pieces can 
function in relative independence. They must be ner- 
vously furnished in such a manner that they can function 
like so many separate organs, that they possess as wholes 
what we have called local responsiveness. This means 
that \)\r reflex a relies of each piece must be united into a 
group, schematically like the groups of reflex arches in 
Figures 18 and 20. We learn from the figures that this 



NODES OF THE CORD 75 

unification of the reflex arches adds a considerable number 
of nervous conductors to those making up each group of 
reflex arches, — conductors which must be found rather 
close together, for the sake of the unifying function in 
question. We must expect, then, to find along the worm, 
here and there, something like clumps or nodes of nervous 
substance. Look at Figure 19, where these nodes are 
apparent. The nervous cord which runs lengthwise through 
the body shows a number of points where something is 
added. Where the cord is a plain cord, the addition is 
simply a swelling, a node, for example, at a. Where the 
cord is a double cord, in the front part of the body, for 
example, at 6, the addition appears as a kind of tie 
between the parallel divisions, giving the whole a 
ladder-like form. These morphological details, of course, 
do not concern us much at present. The important fact 
is that we actually find the addition, at fairly regular 
intervals, of nervous substance to the cord, which con- 
firms our view that the whole nervous cord must be 
organized in successive groups of reflex arches. 

The most conspicuous of these clumps of nervous tissue 
are the two belonging to the head of the worm, at c. It 
may be well to mention that the two parallel divisions of 
the nervous cord are here, between these two nodes, more 
widely separated, in the shape of an oval, because the 
alimentary canal, from the mouth, passes through between 
the two divisions of the nervous cord. If we can speak, 
in the case of the earth worm, of instincts, that is, if there 
are nervous functions sufficiently complicated in their 
sensory and motor aspect and also sufficiently unitary to 
be called instincts, they must be related to the head rather 
than to any other part of the body. The head is, even 
in the earth worm, the most complicated and most im- 
portant motor organ. Food is taken in by the head. 



7(i HUMAN BEHAVIOR 

The direction of locomotion is determined largely by the 
direction taken by the head. The head, therefore, must 
contain many important groups of muscles; but also 
many important sensory points, for the taking in of food 
and the direction of locomotion are determined by the 
nervous stimulations coming from the external objects 
surrounding the head. It is quite natural that all these 
important sensory and motor points must be connected 
by a highly complicated — and therefore somewhat bulky 
— system of nervous conductors, forming out of the many 
reflex arches as many different functional groups with 
manifold interrelations as the life activities of the animal 
require. This, then, is the cause of the accumulation of 
nervous tissue in the head, which far surpasses the accumu- 
lation of nervous tissue at any of the other nodes of the 
cord just mentioned. That there are two such accumula- 
tions in the head is, from our point of view, a mere accident. 
It is, of course, the consequence of the anatomical distribu- 
tion of the head organs. If the anatomy of the head were 
different, both masses of nervous tissue might appear 
united into a single node correspondingly larger. And 
if the anatomy of the head were still different, there might 
be three, four, or more nodes, each correspondingly 
smaller. 

A name for these nodes has long been adopted, which 
we must use here too in order to adjust ourselves to the 
common usage of language. They are called nerve centers. 
We need not discuss the value of this particular name, — 
it has become so common that we cannot escape using it. 
However, it is well to keep any literal meaning of the term 
entirely out of mind. A "center" has no more literal 
meaning for us in the nervous system than a "central" 
has in a telephone system. We know what it is convenient 
to mean by it, in the one case as in the other. It is cus- 



NERVE CENTERS 77 

tomary to speak, not only of nervous centers in general, 
but of higher and lower nerve centers. The significance of 
this distinction can now be easily understood. If a "nerve 
center" is a system of neurons serving the purpose of 
uniting reflex arches into groups and such groups again 
into more comprehensive groups, it must be called the 
higher, the farther removed it is from the sensory and 
motor points of the body. Still, the word center can be used 
in a broader or in a narrower sense. In Figure 20, we may 
call all the neurons enclosed within one of the dotted lines 
a center. Which of them is higher, more removed from 
the peripheral sensory and motor points, is immediately 
clear to the eye. Or, we may take the term center in a 
narrower sense and include only the connecting neuron 
between a central sensory point (for example, S^) and 
its corresponding central motor point (M 2 ah ), and the 
adjoining parts of those neurons which from this central 
sensory and this central motor point run in the peripheral 
direction. In this sense the neuron S 2 ah M 2 ah plus the 
adjoining parts of the four neurons S l a S 2 ah , S\S ah , M 2 h M\, 
M 2 ah M\ would be a nerve center as represented in this 
diagram. (The reader is requested to supply the lettering 
of Figure 20 according to the rules given on page 49.) 
In this narrower sens£ likewise the distinction between 
higher and lower nerve centers is immediately clear 
to the eye. The nerve center of which we just spoke, 
containing the points S 2 ah and M 2 ah , is much lower than 
the nerve center containing the points S 4 and M 4 . It 
seems that we may use the term nerve center in either 
sense without fear that any consequences arise which 
might make our future discussions ambiguous. 

We need not prove that the so-called higher animals 
possess higher nerve centers than the lower animals, for 
the greater complication of their nervous system and the 



78 



HUMAN J5EHAVI0R 



resulting greater complexity of their life activities is the 
very reason why certain animals are called higher in com- 
parison with others which then, of course, are called lower 
animals. But just on account of this fundamental signific- 
ance of the terms lower and higher animals, it is exceeding- 
ly interesting to study the appearance of the bulk of the 
nervous system in a series of higher animals as we have 
studied it in a rather low animal, the earth worm. Let 



#^^>>)Bfe < 



Fig. 21 — Nervous system of a erayfish. 

us now use as an example a crayfish (Figure 21), which 
has a somewhat higher position in the animal scale than a 
worm. There is no essential difference between the 
nervous system of the crayfish and that of the earthworm. 
We notice, however, that the bulky parts of the nervous 
system, the nerve centers, are relatively bigger. This is 
to be expected, since the crayfish has numerous appendages, 
specialized organs which must co-operate for various ends 
and could not co-operate if their systems of reflex arches 
were not combined by connecting neurons into a sufficient 
number of systems of a higher order. 

The vertebrates have their more important sensory and 
motor organs still more concentrated in the head than 
the articulate and lower animals. The reflex arches of 
each of these organs must be united into a group, and 
these groups, again, must enter into manifold combina- 
tions in order to serve the more varied needs of a more 
complex organism. Accordingly we find in the head of a 



THE BRAIN 79 

fish that particularly large accumulation of nerve centers 
which we call the brain (Figure 22). That this group* 
formation of reflex arches, this development of higher 
and higher centers is most conspicuous in the head, is the 
direct result of the greater importance of the sensory and 
motor organs of the head than of the other parts of the 
body. The important reflex arches of the head must be 
well co-ordinated among themselves, but the systems of 
nervous conductors thus formed must also be well co-ordi- 
nated with the less important reflex arches in other parts 
of the body. However, among the latter reflex arches 




A b 

Fig. 22 — Brain of a fish; double view. 

there are a certain class which do not require a particularly 
close connection with the reflex arches of the head. They 
are the reflex arches which serve the so-called vegetative 
or visceral functions of the body. Let us make this clear 
by examples. The approach to a particular article of 
food is controlled mainly by the reflex arches of the head : 
it is a response to sights, sounds, odors received by the 
sense organs of the head. But the approach could not 
take place without the co-operation of the reflex arches on 
which the locomotor organs depend for their function; 
and these organs are to be found in the remainder of the 
body rather than in the head. On the other hand, there 
is scarcely any reason why the intestinal activity of digest- 
ing the food should be enhanced or impaired or otherwise 
influenced during this or any other specially directed 



80 



IIl'MAN BKIIAYIOR. 



locomotion of the body, or why this special locomotion 
should be influenced by the intestinal activity, save the 
extreme cases of an empty or an already overloaded 
stomach, to use familiar language. We are not surprised, 
then, to find in any animal the visceral or interoceptive 
nervous system rather separated from the locomotor or 
exteroceptive nervous system, and to find in the nervous 
accumulation of the head which we call the brain "the 
center" not so much of the whole nervous system as of the 
latter part only, of the exteroceptive system. 

In comparing different vertebrates, let us consider 
of the whole nervous system this part accumulated in the 
head, the brain, alone and compare the relative size of its 
main subdivisions. For this purpose we give to the 
sub-divisions their ordinary names. We notice, in 
Figure 22, that there are five sub-divisions, of which 
three, the frontal ones, are more obviously divided into a 
right and a left part than the other two. To these accumu- 
lations of nervous tissue the term ganglion might be 
applied, as also to any of the bulkier parts of the nervous 
systems of the crayfish and the earth worm in Figures 
21 and 19. Or they may be called lobes, a tern frequently 
applied to sub-divisions of the brain. Thus, in Figure 22, 
ol means "optical lobe," of "olfactory lobe." In the 
same figure m stands for the "medulla," joiifing the cord, 
also called bulb because of its shape, cb for " cerebellum " 
or small brain, CER for "cerebrum" or large brain. 




Fig. 23 — Brain of a frog; double view. 



GROAYTH OF THE CEREBRUM 



81 



Compare with these ganglions of the fish the same 
ganglions of the frog, as shown in Figure 23. Their 
relative size has changed in favor of one, the cerebrum. 
This is still more obvious in a still higher animal, a bird. 




A B 

Fig. 24 — Brain of a bird; double view. 

The two halves of the cerebrum, the so-called hemispheres, 
are now, especially in the view of Figure 24, J5, the most 
conspicuous part of the whole. The same development 
continues when we pass, in Figure 25, to a mammal. 
The hemispheres of the cerebrum begin to look as if they 
were the whole brain. The optical lobes have indeed 




A B 

Fig. 25 — Brain of a lower mammal; double view. 

been so completely overlapped by the ever growing 
hemispheres that they have disappeared from sight. This 
continued growth of the same single ganglion — quite 
aside from a continuous, but less marked growth of all 
others — through the various stages of evolution of the 
vertebrates illustrates a principle different from that 



82 



HUMAN BEHAVIOR 



which requires a bulkier nervous system for an animal 
possessing a greater number of sensory and motor points. 
This continued growth of a single ganglion can have a 
meaning only if the ganglion thus growing does not serve 
any peripheral points directly, but exclusively indirectly, 
by interconnecting unified neuron groups and unifying 
them into secondary and further derived groups, as shown 
diagrammatically in Figure 20. The growth of this 
ganglion, then, enables the animal more and more to 






A 



B 




Fig. 26 — Nervous system of man; double view. 



THE HUMAN BRAIN 83 

react at any motor point to an excitation occurring at any 
sensory point whatsoever, without losing its indispensable 
local responsiveness. 

If we compare (Figure 26) the bulky part of the nervous 
system of man, that is, the part which can be cut out of 
the body with comparative ease, and the bulky part of 
the nervous system of a worm (Figure 19), we see that 
they are not unlike in appearance except for the fact 
that to a nervous system like that of the worm man has 
added the enormous mass of nervous tissue of the cerebral 
hemispheres (and, we might add, to a lesser extent the 
cerebellum) serving no other purpose than that explained 
in the last paragraph. Along the two sides of the spinal 
cord, in Figure 26, there are two rows of ganglions some- 
what separated from the cord. They obviously group 
the reflex arches of each side and thus make the organs 
on one side of the body relatively independent of each 
other and of those of the other side. Many of our activi- 
ties, it is true, are of the symmetrical kind, requiring 
co-operation of the motor organs symmetrically situated. 
But not a few of our activities are one-sided. The reflex 
arches of a certain region of either side are therefore united 
in a ganglion before coming into connection with the 
nervous conductors of the spinal cord. 

Figure 27 shows the enormous development of the 
cerebral hemispheres in man as compared with those of 
the lower vertebrates represented in Figures 22, 23, 24 
and 25. The cerebrum has grown to such an extent that 
it hides practically all the other parts of the brain, so 
conspicuous in the fish, the frog, and the bird. The 
cerebral hemispheres, which in the mammals have fallen 
sideways over the other original ganglions of the brain, 
have further grown especially in the forward direction, 
thus covering their own lateral parts and forming the 



St 



HUMAN BKIIAYIOR 



large Sylvian fissure (at S in Figure 27). Only toward the 
back a piece of the cerebellum is still left uncovered. 
The cerebrum has become practically the whole brain. 
Its growth, taking place in the brain exactly there where 
the most pronounced growth took place during the im- 
mediately preceding period of evolution, has every time 
served to make possible interconnection of the highest 
centers by still higher centers, thus bringing about an 
ever increasing possibility of any imaginable group of the 
seemingly most unrelated motor points being functionally 




Fig. 27 — Brain of man; double view, 
governed by any group of seemingly most unrelated 
sensory points. We need not suppose, however, that in 
this process of complication identical with unification, 
evolution has reached its highest possible mark. We 
should over-estimate our race if we thought so. There 
are many indications — some of them we shall have to 
mention later — that the functions of innumerable reflex 
arches and groups of reflex arches are even in the human 
race still practically independent of, never governed by, 
the function of those, belonging to the majority, which 
arc already effectively unified by their connections with 
the brain and especially with the cerebral hemispheres. 



SEVENTH LECTURE 

Learning. The susceptibility of nervous conductors. 
Variations of the nervous path. (1) Two kinds of variation 
of response. (2) Sensory condensation. (3) Motor con- 
densation. Graceful motion. Inhibition. How a child 
comes to fear a fire. 

THUS far we have spoken of animal activities 
only under two heads, as reflexes, and as 
selected groups of reflexes, that is, instincts. 
Both these kinds of activities may be given 
a common name. We may call them hereditary activi- 
ties, because the characteristic response following 
each particular stimulation is in these cases com- 
pletely determined by the strictly biological inheri- 
tance of the individual from his ancestors, — is in no way 
shaped by the geographical and social inheritance resul- 
ting from the fact that the individual has been given by 
his ancestors life and the training of his youth in a particu- 
lar geologic-physical and social environment. This shaping 
during life of the individual's manner of acting may be 
referred to by the word "learning," or by the word 
"habit." We are, perhaps, inclined to use the word 
"learning" chiefly in connection with social institutions, 
"schools" of all kinds, "habit" chiefly in connection with 
altogether fortuitous circumstances. For us, however, 
in this treatise, these words are synonymous. Regarded as 
phases in the behavior of the human or animal individual , 

85 



86 HUMAN BEHAVIOR 

acquiring a habit and learning are identical. In each 
animal we find — the higher the species to which the indi- 
vidual belongs, the more numerous — learned or habitual, 
in addition to hereditary, activities. Our next task is 
the description of the changes which hereditary nervous 
activities undergo in order to become habit, — the descrip- 
tion of the process of learning, or rather, of the various 
kinds of processes of learning. 

It is plain that any shaping during life of an individual's 
sensori-motor activity presupposes: first, that there is a 
variation in the succession of sensory excitation and motor 
response, and secondly, that this variation is fixed and 
thus caused to reappear. The variation is possible only 
if the main flux of the excitation once takes a path differ- 
ent from the one which is to be expected according to 
the shortest hereditary connection of sensory and motor 
points. The fixation of this path is possible only if 
(we might also say: fixation means that) nervous conduc- 
tors are in some way susceptible to excitations traveling 
through them, so that one of the reasons why an excitation 
may be thought to choose a particular path, is simply 
this, that it has once before taken this path. Of course 
this statement may, and must, be made more definite 
with respect to our assumption that the main path of 
the nervous flux is the path of least resistance. We must 
say, then, that the susceptibility of nervous conductors 
consists in their resistance being reduced by a flux occur- 
ring in them,— this resistance to stay reduced for a consider- 
able time after the flux has terminated. We may add, 
at once, remembering that the counterpart of learning is 
forgetting and thai forgetting is a gradual process: that 
we have the right to assume that the reduced resistance 
of any nervous conductor slowly rises again to its original 
measure. 



NERVOUS SUSCEPTIBILITY 87 

The question then is: do the pictures of streaming 
which we have used in order to have before our mind a 
clear idea of nervous activity and its peculiarities, aid us 
also in imagining the susceptibility of a neuron as one of 
its natural properties? It seems that this question can 
be answered unhesitatingly in the affirmative. We are 
hardly more familiar with any other natural event than 
that of a stream broadening, washing out its channel; 
and a dry river bed being gradually obliterated by being 
filled with debris and dust is not a very unusual phenom- 
enon either. Our picture of nervous activity, with regard 
to the susceptibility of conductors, is therefore quite consis- 
tent. The question is then left, if it is also consistent 
with regard to the possibility of a variation of the main 
path along which the excitation is conducted. Now, this 
question has been answered already, in our discussion of 
instinct. We said that an instinct is not only a collecting, 
but also a selecting agency, and we explained the selection 
of a path for an excitation, by referring to the familiar 
physical principle underlying the action of a jet-pump. 
No further assumption is necessary, only a reference to 
an assumption already made. A variation of the main 
path taken by an excitation can, accordingly, be the result 
of a second nervous process deflecting the first by dint 
of its own greater intensity. That a variation of the ner- 
vous path can be brought about also by other factors, with- 
out any deflection, will appear later. 

We may distinguish several classes of variation of the 
nervous path. If the stimulation as well as the motor re- 
sponse is so simple that the whole nervous activity can be 
called a reflex, the variation of the nervous path can consist 
either in the motor response occurring at a motor point 
which is not the point corresponding to the sensory point 
stimulated or in the very same motor response following 



88 HUMAN BKIIAYIOR 

tlu 4 application of a stimulation to a point which is not 
the corresponding sensory point. Let us use variation 
of response as a technical term for this kind of variation 
of the nervous path. Naturally, we can apply the same 
term also to cases in which the nervous path is neither at 
its sensory nor at its motor end quite so simple. Indeed, 
looking for a striking concrete example, we can hardly 
help giving one in which the nervous path is complex. A 
small child, taking beer into his mouth, spits it out, 
reflexly, — or rather instinctively, for the motor activity 
may be quite complex. Any bitter substance stimulates 
definite sensory organs of the mouth, and the motor res- 
ponse of the facial and other muscles is that which we call 
spitting. The bitter substance is thus removed. The 
large number of people who habitually drink beer can have 
acquired this habit only by a variation of response taking 
place and becoming fixed. Once, instead of spitting, 
the very different motor response of swallowing occurred, 
as a variation, and this variation, becoming fixed, became 
the habit of drinking beer. In this example a different 
response came to follow the same stimulation. As an 
example of the same response following a different stimu- 
lation we may mention this. A baby, during the first 
three or six weeks of his life, responds to any sudden noise 
by quickly closing his eyes. It is easy to observe this. 
One need only clap his hands or whistle in order to see the 
baby wink. On the other hand, one may closely approach 
the baby's open eye with a finger or a stick without caus- 
ing the slightest winking, unless the eye is actually touched. 
When the baby is a few months old, all this has changed. 
Noises rarely call forth the response of winking, but 
when any object is brought near the eye, the latter is 
closed. This reaction then remains our habit all through 
our adult life. Once, of course, the variation must have 



VARIATION OF THE PATH 89 

occurred for the first time, — the variation of the nervous 
path which consists in a visual stimulation taking the 
place of an auditory stimulation, while the motor response 
remains the same. 

If the stimulation is complex and the motor response 
correspondingly complex, the variation of the nervous 
path can consist in the complex response being called out 
by a greatly simplified stimulation, possibly a stimulation 
of a single sensory point. The habitual nervous activity 
then becomes similar to an instinct, for a complex reaction 
in response to a simple stimulation is, as we have seen, 
characteristic of an instinct. In order to have a brief 
term for this kind of a variation of the nervous path, let 
us call it sensory condensation, thus referring to the fact 
that at the sensory end of the system of nervous conductors 
the flux (when represented reversely in a diagram) no 
longer spreads out, but is condensed into a narrow channel. 

An example, rather complex in all its aspects, but very 
familiar and therefore well illustrating our case, is the 
following. In playing a certain piece of music on the piano, 
at a particular place in the music each one of several fingers 
has to perform a definite movement, — what movement, is 
indicated by as many notes as there are fingers to move. 
The beginner, in order to strike the correct chord, looks 
at every note. But after some time of practice, we observe 
that he plays exactly the same complicated chord even 
when some of the notes, without his knowledge, have been 
erased or changed by us. Obviously these notes are no 
longer needed for the response, and a simpler stimulation 
now brings about the same motor response. Typewriting, 
reading, proofreading, weaving, attending to any machine, 
— any kind of skillful activity can illustrate this same kind 
of variation of the nervous path. The complex activity 
is ultimately called forth by a part of the original stimu- 



!)() HUMAN BEHAVIOR 

[at ion; sometimes to the detriment of the subject, as when 
a proofreader overlooks a typographical error, reading the 
whole word although not all of the word is there to act 
on his eyes. 

If the motor response is complex (because it is an in- 
stinctive response or the stimulation is complex), the 
variation of the nervous path can consist in the response 
being greatly simplified, possibly reduced to a response at 
a single motor point. Thus it would become similar to a 
reflex response, were it not, perhaps, for the complexity of 
the stimulation. In order to have a brief term for this kind 
of variation of the nervous path, let us call it motor con- 
densation, thus referring to the fact that at the motor end 
of the system of nervous conductors the flux no longer 
spreads out, but is condensed into a narrow channel. 
Watch a child receiving his first instruction in writing 
and you will frequently observe, not merely a moderate 
activity in the shoulder, wrist, and finger joints, as when 
an adult is-writing, but in addition to an excessive activity 
in these joints a tense bending of those fingers of the writing 
hand which do not hold the pen, and also of the fingers 
of the other hand, even a twisting of the head and the feet 
as if no writing were possible without them. We say in 
such a ease that the person acts awkwardly. The dis- 
appearance of awkwardness is generally equivalent to 
the dropping of all movements unnecessary for the end in 
question. A graceful motion is simply a motion no ele- 
ment of which appears to be superfluous. The acqui- 
sition of graceful motion means motor condensation. 

OF course, our distinction of three classes of variation 
of I lie nervous path, variation of response, sensory conden- 
sation, and motor condensation, does not imply that 
each of these variations must occur in separation from 
the others. On the contrary, we must expect to find 



INHIBITION 91 

in actual life usually mixtures of them. As example of 
such a mixture may serve the behavior of a person falling 
into a river. If this is his first experience of the kind, 
the motor response is exceedingly complex. The hands 
move about in all directions, but chiefly they are thrown up 
in wild attempts to catch anything which might be in 
reach — a straw, as the proverb says — while the feet make 
movements which, when slowly executed, might be useful 
in climbing a tree, but which can serve no very useful 
purpose in the surrounding fluid. The skillful swimmer, 
on the other hand, merely makes a few moderate down- 
ward strokes with his outstretched arms and hands, 
and thus reaches the surface and stays there, possibly 
not moving his feet at all. The variation of the nervous 
path in this case obviously consists in a variation of 
response as well as a motor condensation. As a matter 
of fact, a sensory condensation is also involved, for during 
the process of learning to swim many stimulations of 
various sensory points (perhaps a teacher's words and 
example) are effective, which later become superfluous. 
The process of learning, the acquisition of a habit, has 
a negative aspect of great importance, so far as the motor 
end of the nervous activity is concerned. What a person 
does not do, whether he reacts towards his physical or 
social environment in a definite way or remains inactive 
in this way, is frequently of the greatest consequence to 
others. When I am walking along a highway and meet 
strangers, my chief interest is in not being attacked 
and robbed. What they positively do, concerns me but 
little, possibly not at all. How important the negative 
aspect of human activity is appears from the fact that 
the great moral law of the decalogue contains almost 
exclusively negative rules. Our scientific interest, therefore, 
can not be restricted to the positive aspect of an individual's 



<)2 HUMAN BEHAVIOR 

motor activity, It is clear, even from the mere outline 
of nervous activity as given thus far, that the negative 
aspect of the motor result of a nervous process can 
never be a reduction of a nervous excitation to nothing, 
but only a deviation to a motor point other than the 
one at which we had a certain right, according to our 
knowledge of the nervous connections, to expect its 
motor response. When we are interested in a person's 
or animal's not doing a certain thing, we use as a tech- 
nical term the word "inhibition." From the point of 
view of this treatise, inhibition means that the indi- 
vidual does something else instead of what we thought 
or feared he might do, while we do not care what it is that 
he actually does. From a purely neurological point of 
view r the term inhibition in this sense is superfluous. 
Nevertheless we shall have to use it because of its great 
significance from the social point of view, for many social 
institutions of great importance, for example all those 
connected with crime and criminal law, cannot do without 
this concept of inhibition. The law which inhibits murder 
by stating "Thou shalt not kill" does not state what we 
shall do instead of killing. The law giver is not concernec 
with our action provided it does not consist in killing. 
But it is of great value to us in any sociological application 
to be aware of the fact that, at the bottom, the prevention 
of crime is not a problem of preventing action, but alto- 
gether a problem of substituting sl socially valuable reaction 
to a certain stimulation for a socially harmful reaction. 
Thus far, we have hardly done more than define the 
terms, variation of response, with its negative aspect 
inhibition, sensory condensation, and motor condensation. 
We must now make clear in detail, in specific instances 
illustrating these cases, what goes on in the nervous sys- 
tem when the nervous path is modified and this modifica- 



EDUCATION 



93 



tion becomes fixed, — to make sure that the fundamental 
assumptions hitherto put down are sufficient for an under- 
standing of the behavior of any animal, even the highest, 
or that they must be supplemented in a particular way. 
Let us study in detail, first, the fundamental nervous 
processes underlying the "education" of the proverbial 
child who learns to fear the fire. This is a variation of 
response. The instinctive activity called out by the flame 
impressing the sensory points of the eyes consists in 
a drawing nearer of the body or its limbs to the flame. 
The habit which exists in later life is a withdrawing of 
the bodv or its limbs from the flame. The variation 



S^ fingerTi 




M 



Drawing in 1% Ma Stretching out a 

Fig, 28 — Burnt child fears the fire. 



of the nervous path, therefore, must consist in this, that 
the excitation coming from the eyes, which at first 
ses into certain muscles, for example, those stretch- 
ing out the arm, later passes into the very antagonis- 
tic set of muscles, drawing in the arm. In Figure 28 we 
represent this schematically as if the eyes stimulated 
were only a single sensory point (S a ) and each of the 
muscle sets only a single motor point {M a approaching, 
M receding). The only difference from our previous 
method of drawing the figures is that the two reflex arches 
open in opposite directions, right and left, instead of both 



94 HUMAN BEHAVIOR 

downwards. S a and M a are corresponding points. It 
is natural, therefore, thai the child's finger is stretched out 
toward the light. The problem is how we can explain 
that later the path ^ a t>\^ 2 ab M 2 ab M l b M b , marked in the 
figure by a zigzag line, has a lesser resistance than the path 
S a S a M a M a , so that then the finger is withdrawn as soon 
as tin 4 fame becomes simply visible. We have stated 
that such a change must mean the fixation of a variation, 
and this variation may be the result of a second nervous 
process deflecting the first one from its original course, 
in the direction of M a , to another course in the direction 
of M b . The second nervous process, therefore, must 
have M b as its motor end. What kind of a sense organ 
is then represented by the sensory point S b , corresponding 
to this motor point M b ? We know that the drawing 
of limbs toward the body, while resulting from many differ- 
ent stimulations, is especially the result of pain stimulation. J 
An animal suffering from strong pain of any kind does 
not stretch out its limbs, but draws them in, curves them, 
and the whole body too, if possible. It writhes. We know 
further, from direct and indirect experience, that pain 
stimulation is quite generally the essential factor in any 
kind of variation of response. S b represents, therefore, the 
pain nerve ends of the finger stretched out. In what way, 
then, in our diagram of Figure 28, do the two nervous 
processes, from the eyes and from the finger tip, influence 
each other? 

In order that one of two nervous processes deflect the 
other from its course, they must obviously exist in 
the nervous system (Figure 28) simultaneously. This 
does not imply, however, that one of them may not begin 
before the other. In our case, S a is stimulated first, 
and only because of the excitation traveling from S a toM a 
and causing the finger to approach the flame, occurs 



BURNT CHILD 95 

stimulation of S b by the flame. From this moment on 
S a and S b are stimulated simultaneously. Whether 
now the finger is moved into the flame or away from it, 
depends, so far as it is a strictly mechanical event, simply 
on the relative force with which the one (at M a ) or the other 
(at M b ) of the antagonistic sets of muscles contracts. 
This muscular force here depends on the relative intensity 
of the nervous flux towards M a and towards M b . It 
seems rather obvious that the excitation at S b , caused 
by the burning of the finger in or near the flame, must be 
exceedingly strong, so that, as a purely mechanical effect, 
the reaction must be that of a withdrawal. But even 
if the two reactions were not as mechanical phenomena 
mutually exclusive, — even if they were riot antagonistic, 
but anatomically independent movements, — the laws of 
nervous function alone would practically suppress the one 
in favor of the other, because the stronger nervous process 
would sufficiently deflect the flux of the weaker nervous 
process. It is this suppression of one nervous process 
by another nervous process (and not at all the mechanical 
annihilation of one muscular pull by another) which we 
are here concerned with. Let us see how this is brought 
about. 

The flux originating from S a divides at the point S*. 
The larger part of it takes the path S\M\\ a smaller 
part the path S l a S 2 b M 2 b Ml, because the resistance 
of the latter is, according to the diagram, three times 
that of the former. It is evident that at the point M 2 ab , 
too, a division of the flux must take place. Although the 
resistance of the path M 2 ab M\M b is no greater than that 
of the path M 2 ab M\M a , most of the flux must go on 
from M 2 ah in the direction of Ml, because the flux over 
Si M a M a , according to our assumptions, acts as suction 
upon the contents of the conductor M 2 ab M l a , whereas 



96 HUMAN BEHAVIOR 

DO similar force acts in the direction of Ml. Practically 
all of the flux which originates from S a finds its outlet 
therefore in M n only an insignificant fraction going to M b . 
But immediately the excitation of the point M a brings 
about the strong stimulation of S b , the outstretched 
finger being burnt. A strong flux now goes on from S b 
to M b , mostly over S\M\, partly over S\S 2 ab M 2 ab Ml; 
but even the part taking the latter path is strong compared 
with the flux originating from S a . At once all the condi- 
tions are changed which determine the flux originating 
from S a . The strong current over SlS 2 ab M 2 ab draw r s the 
contents of the conductors S^S 2 ^ and S a S\. Consequen- 
tly most of the flux from S l a takes the direction of S 2 b \ 
little takes the direction of M l a . From M 2 ab , again, most 
of the flux is drawn, by the strong current over SlMlM b9 
in the direction of Ml; little in the direction of Ml, since 
the weak current over S l a M l a M a draws only weakly in 
this direction. All this will appear even more natural 
to us when we recall that in our physical analogy, the 
jet-pump, the suction effect is not simply proportional 
to the velocity of the fluid, but to the square of the velocity. 
We have the right to assume, therefore, that the flux of a 
weak nervous process is very readily consumed by the 
deflecting effect of one which is only considerably stronger. 
Consequently, in spite of the continuance of the stimula- 
tion at S a (the eyes), there is now practically no motor 
excitation at M a (no tendency to stretch out). 

How is the fixation of this variation brought about, 
to the effect that later, when *S a is stimulated, the 
response occurs at M b , without any stimulation at all 
occurring at S b ? We have assumed that each neuron 
is susceptible to any flnx occurring within it, so that its 
resistance is lessened in proportion to the flux and the 
time during which it continues. Under the assumption 



FEARS THE FIRE 97 

of such a susceptibility the fixation of the variation of 
response is a plain enough matter. The direct path 
from S a to M a is made up (in the diagram of Figure 28) of 
three units of length, the path from S a to M b of five units. 
The reduction of the resistance of the latter path need not 
be by any means enormous, in order to make the flux in 
the direction of M a so weak as to be practically insignificant. 



EIGHTH LECTURE 

Substitution of a direct for a devious nervous path. 
Nervous tension inducing growth. Automatic action. Peri- 
odic levels of learning. Two meanings of forgetting. Pos- 
itive and negative susceptibility of neurons. The curves 
of learning and forgetting. 

THERE is, concerning the fixation of a new 
path, a very important problem still left. 
We have reason to believe that in addi- 
tion to the fixation just mentioned, there is 
another kind of fixation. Consider this example. 
When we ask an educated person what six times 
seven is, the answer is forty-two. When we ask 
him what six times seventy-seven is, the answer 
is four hundred and sixty two. Either answer will 
doubtless be given with the same definiteness and 
correctness. But there is a great difference in the prompt- 
ness. While the first answer is enounced directly, the 
second is enounced only after a considerable delay. 
The explanation seems obvious. Either path is somehow 
fixed, but the former, because of the promptness of the 
response, seems to be much shorter than the latter. As 
we have just seen, a new path resulting from a variation 
by deflection is naturally a relatively long path, since 
the possibility of variation depends on the mediation of 
centers higher than those of the path to be varied. The 
fixation of the new path in the manner described does not 

98 



DEVIOUS PATHS 99 

change its length and can not, therefore, change the time 
interval between the stimulation and the response, — the 
so-called reaction time. Thus, there must be a second 
kind of fixation of a path, which implies a shortening of 
the path. We can explain this by the aid of a compara- 
tively simple hypothesis. This hypothesis must be 
the assumption of a property of the nervous system 
which permits the growth of neurons in places where there 
were previously none, and thus the shortening of a long 
path by substituting a direct path for a devious and round- 
about one. The neurological facts known, point indeed 
in the direction of such an assumption. 

All growth of living tissues, alike in the vegetable and 
animal world, is of either one or the other kind, by cell 
division or by growth of the individual cells. Different 
kinds of tissues, however, show a remarkable difference 
with respect to these two kinds of growth at the different 
ages of an animal. In certain tissues, cell division can 
occur all through life. The necessity of this in certain 
tissues is clear, for example, in those tissues of which our 
skin consists. When we have received a considerable 
wound, involving the loss of some skin, the cells at the 
edges of the wound divide. The resulting new cells 
increase in size and divide again ; and so on until the opening 
is completely covered with new skin. Without cell 
division any new skin could hardly be formed, since there 
is a limit to the size which individual cells may normally 
attain. But scarcely any animal goes through life without 
frequently receiving wounds. In other tissues cell divi- 
sion becomes impossible after the animal has reached a 
certain age. Since the muscles are of special significance 
for animal behavior, let us take the muscles as an 
example. It seems that in human muscles cell division be- 
comes impossible after the age of from twenty to twenty- 



100 HUMAN BEHAVIOR 

five years. From this follows the important fact that, in 
order to become an athlete, a person must exercise his 
muscles and thus induce both cell division and cell growth 
before the age of twenty-five years at the latest. If 
he has failed to do this, the number of muscle cells 
which he possesses is so small that exercise, because of the 
limited growth of the individual cells, will now only slight- 
ly increase the bulk and therefore the total strength of 
his muscles. This age limit for cell division differs in 
tissues of various kinds. 

The bulk of the nervous system consists of nervous 
tissue proper, that is, the conducting tissue, and of suppor- 
ing tissue. In the latter, cell division may occur at any 
age. In the nervous tissue proper, however, cell division, 
that is the multiplication of neurons, stops before man 
begins his postnatal life. It has been found that about 
three months before birth man has as many neurons as 
he will ever have in his life. At this time, however, the 
vast majority of these neurons are in the undeveloped 
condition which we have already described. They are 
little balls without any branches and therefore of little 
value for the conduction of any excitation. They 
develop into complete conductors at various times during 
life. Some develop early, in order to serve those muscular 
activities which the baby needs immediately on entering 
into life, for example, the activities of sucking and swallow- 
ing. Others develop during the succeeding years of child- 
hood and youth. It is a peculiar fact, however, that 
even in old age there are still many undeveloped neurons 
present in the human brain. The conclusion offers itself 
that these undeveloped neurons enable their owner to 
acquire, even at an advanced age, certain new nervous 
functions. The numerical possibility that such unde- 
veloped neurons will always, to the time of death, be 



UNDEVELOPED NEURONS 101 

present and ready to take service, appears from the 
fact that the total number of neurons in the human brain 
is enormous, uncountable. They have been estimated 
at from three to four thousand millions. How long would 
it take us to count so high, if it took but a second to pro- 
nounce each successive number? A day of twenty-four 
hours contains 83,400 seconds, a hundred years only 
3153§ million seconds. We could not do the counting , 
in a life time. Thus it does not matter much if we take 
a few millions of undeveloped neurons with us into the 
grave, provided that we are thus at any time of our life 
capable of new adaptations, of new useful habits. Capable 
also of regaining nervous functions which we have lost 
in consequence of a lesion within our brain, — say, a bullet 
having passed through our brain. In such a case, if we 
are lucky enough to remain alive, we are found to be inca- 
pable of performing certain skilful movements and of 
reacting in any way to certain stimulations. If a piece 
of our brain is destroyed, it does not regenerate like a 
piece of our skin. Its room is filled out with supporting 
tissue, but the nervous tissue proper, the neurons lost, are 
lost forever. The functions lost, however, may be entirely 
or partly regained, just as if they were new habits. 

We found it necessary to assume that a new nervous 
path, a variation by deflection, may first be fixed in 
its original length and later greatly shortened. We 
can now explain how this shortening fixation can come 
about. Suppose a new habit is being formed by the 
variation of a path, leading now, instead of to the point 
M P which corresponds to S P (Figure 29), by way of a 
higher center to a non-corresponding point, say M q . 
S p and M q are supposed to belong to two reflex arches 
which are very remotely connected, over central sensory 
and central motor points of a very high order, so that the 



10* 



HUMAN BEHAVIOR 



resulting path is of a very round-about and zigzag nature. 
Figure 29 may be regarded as diagrammatically represent- 
ing this path,without, however, suggesting that the path in 
the brain would actually present itself to the eye as a 
symmetrical figure like this. What is important in the 




Fig. 29 — Automatic action : Short-circuiting in the nervous system. 



diagram is only that in various places, for example, at 
S p , two points of the path are by chance very near each 
other. Let us assume that in such a case we have between 
the two points a peculiar, growth inducing, biological 
condition, just as we should have, if the path were a 
metallic conductor carrying a high potential current, an 
electrical tension likely to break through the insulating 
substance in sparks. This simple hypothesis is sufficient 
to explain the second kind of fixation of the variation of 
a nervous path. The biological tension, so to speak, 
between Sp and M\ causes one or more of the undeveloped 
nerve cells to grow and send out branches in either direction 
of the tension. The consequence of this development 
of a new connecting neuron is a shortening of the path 
leading from S p to M q by practically putting out of func- 
tion the part above Sp M\ , owing to the higher resistance 



SHORT-CIRCUITING 103 

of this upper loop. The result of the new growth is that 
the response at M Q to stimulation of S p occurs with greater 
quickness and also with greater definiteness, exclusiveness, 
for less of the flux from S p can now reach motor points 
other than M Q . 

The same kind of shortening of the path may occur 
later between S^ and M\. Here again the biological 
tension may cause the development of a new connecting 
neuron out of an undeveloped nerve cell. The length of 
the total path leading from S p toif 2 may thus be reduced 
to almost that of a reflex arch. The response at M q to a 
stimulus at S P must then occur with the same quickness 
and definiteness as a reflex. That habits can become 
very much like reflexes is well known. In the drilling 
of a soldier good examples can be found by any observer. 
Action of this kind is called automatic. It scarcely 
differs from reflex action in any respect, save in its origin, 
which is not hereditary. Its resemblance to reflex action 
is illustrated also by the resistance which automatic action 
offers to the destructive influences of certain diseases 
of the brain. When a nervous disease has made a man's 
actions entirely illogical, certain automatic actions still 
occur with the same promptness as most reflexes, for 
example, oaths — in people who have acquired the habit 
of swearing in early life. This indicates the probability 
that our hypothesis agrees with what actually occurs 
in the brain. Since the disease attacks the higher centres 
of the brain before the lower centres, the development of 
automatic action seems to consist in the functional 
cutting out of higher centres from the path, as explained 
in the diagram of Figure 29. 

If the distance between S 2 P and M\ had been less than 
between S p and M\, the shortening of the path might 
immediately have occurred here. This possibility agrees 



104 



HUMAN BEHAVIOR 



with the observation that habitual reactions whose per- 
formance at first requires a considerable reaction time, 
are sometimes made quicker only in numerous stages, some- 
times become completely automatic almost at one time. 
Our whole view T concerning the shortening of a newly 
acquired nervous path is thus supported by innumerable 
experimental studies in the acquisition of skill, for example, 
in typewriting or in telegraphing. If the growing efficiency 
of a person learning to write on the machine is represented 
in a curve, we do not obtain a constantly rising curve, 
but one which rises to a certain level, remains on this level 
for some time, rises to a higher level, remains on it for some 
time, and so on, as illustrated in Figure 30. Such an im- 




Fig. 30 — Steps in acquiring skill: Periodic levels of learning. 

provement by steps is to be expected if the fixation of the 
variation of response is not merely a fixation of the new 
path over higher centers, but at the same time a repeated 
shortening by cutting off loops from the original winding 
path. Each time when a loop is cut off, the test of the 
person's efficiency must reveal a rather sudden improve- 



LEVELS OF LEARNING 105 

ment. After this improvement, however, the efficiency 
cannot but remain practically stationary, until another 
neuron, perfecting its development, cuts off another loop 
and thus raises the efficiency rather suddenly again to a 
higher level. 

Let us return to what we called the susceptibility of 
the neurons. On it is based every possibility of a variation 
of the nervous path, that is, every possibility of learning. 
We know that the opposite of learning, forgetting, is of 
as much consequence in actual life as learning. If we 
call forgetting the opposite of learning, we should do so in 
only one sense, namely, in so far as a path, instead of 
becoming fixed, is being obliterated. In another sense 
the opposite of learning, of a new reaction more useful 
than the old, is a new reaction less adapted to our needs 
than the old, as when we "forget" to lock the door in 
leaving our house. This, obviously, is a case of inhibition, 
of nervous deflection, rather than of true forgetting. In 
so far as obliteration is opposed to fixation we are inclined 
to explain obliteration by a property of the neurons 
similar, but opposite to that on which fixation is based. 
We might speak of a negative as well as of a positive 
susceptibility. We said previously that the susceptibility 
of nervous conductors consists in their resistance being 
reduced by a flux occurring in them, and added that the re- 
duced resistance of any nervous conductor very slowly rises 
again to its original measure. The reduction may be called 
positive susceptibilty since it is a reaction to function, the 
rise negative susceptibility since it is a reaction to a lack 
of function. 

In accordance with our statements thus far, the magni- 
tude of the positive susceptibilty must be determined by 
two factors, the intensity of the nervous process and its 
duration. In the analogous case the river bed is washed 



106 HUMAN BEHAVIOR 

out the more, (1) the more water flows through it 
in a unit of time, and (2) the longer this flow continues. 
On the other hand, the negative susceptibility depends 
only on one factor, the time during which no ner- 
vous process occurs in the neuron. It is interesting, 
therefore, to compare the quantitative results of experi- 
mental studies of the progress of learning, which is the 
effect of the positive susceptibility, with those of the prog- 
ress of forgetting, which is the effect of the negative 
Mi^ceptibility. 

The increasing efficiency of reaction in the process of 
learning is always represented by a curve like that of 
Figure 31, rising first rapidly, then more and more slowly, 




Fig. 31 — Learning dependent on time. 

provided that we have in mind one continuous process 
without any intervening periods of rest. In a longer 
process of learning spreading over days or months, and 
containing many extended periods of rest, the efficiency 
rises, as we have seen, in the manner of Figure 30. 
We notice that in a continuous process of learning, lasting 
say, half an hour, the first few minutes are the most 
valuable. During the following minutes less and less 
is gained in efficiency, and the last few minutes add so 
lit tie to the result that we might just as well have stopped 
earlier. This fact is established beyond doubt by experi- 
ment and agrees also with the ordinary experience of 
any one who has to practice anything, for example, the 



LEARNING AND FORGETTING 



107 



school-boy memorizing a foreign vocabulary. To read 
over the whole task five minutes a day for a sufficient 
number of days to complete it, is much more economical 
with regard to the total time required, than to complete 
the task in one continuous memorizing. If we continue 
the process only for five minutes, we do not make use of 
the uneconomical part of the time curve farther to the 
right in the figure. At first glance, the facts represented 
in this curve seem to overthrow our analogies. Why 
should a flux, broadening and deepening its channel, 
do this the longer the less? But the matter becomes clear 
when we remember that in a neuron, with its limited 
resources, the flux cannot remain continuously on the 
same level of intensity. The neuron does not become 
less and less susceptible to the flux, but the flux becomes 
in spite of an undiminished intensity of stimulation less 
and less intensive. The total result, then, must be in 
accordance with Figure 31. 



iciency 




Fig. 32 — Forgetting dependent on time. 

The decreasing efficiency of reaction in forgetting is 
represented by a curve like that of Figure 32. This 
agrees well with our analogies. We compared the negative 
susceptibility with the fate of a river bed through which 
no water flows any more, and which is gradually obliterated 



108 



HUMAN BEHAVIOR 



by being filled with debris and dust. Such a filling in is 
usually very pronounced at first, when the banks of the 
river bed are still steep, less and less considerable later, 
so that traces of the original depression of the ground 
may continue for an exceedingly long period. Although 
the analogy is remote, it shows that the curve may well 
be expected to have the shape of Figure 32. 

This curve, however, of Figure 32 does not indicate 
what changes, if any, the efficiency undergoes during the 
time directly following the period of practise, during the 
first few seconds or minutes, let us say. Now, it is a 
matter of common experience, that anything we have 
just learned stays with us, as a rule, for a few minutes 



Effici 



enc 



y 



Time 
^ 



Fig. 33 — Forgetting immediately after practice. 

with hardly lessened efficacy and is only then forgotten 
at a rapid rate. Perhaps the complete curve ought to 
be drawn as it appears in Figure 33, remaining almost 
on a level for a short time, then falling very quickly and 



NO IMMEDIATE FORGETTING 109 

later falling more and more slowly. The usual experiments 
concerning the rate of forgetting do not tell anything 
about the first few minutes since they are made only 
with the intention of recording the loss from day to day. 
But the ordinary experience is in this case definite and 
general enough to assume that the loss during the very 
first few minutes — not to speak of seconds — is practically 
nothing. Let us here record the fact without attempting 
to explain it. 



NINTH LECTURE 

Sensory condensation in piano playing. Proportional 
reduction of the resistance of higher and lower centers 
connecting the same corresponding points. The positive 
(and negative) susceptibility of a higher center greater than 
that of a lower center. Motor condensation in grasping. 

WE have studied and explained in de- 
tail one of the three kinds of varia- 
tion of the nervous path, the simple 
variation of response. Let us study 
next that kind which we called sensory conden- 
sation. Musical practise may serve as an example. 
A child learning to play the piano, at a certain place in 
his piece, wants to strike two keys without having to look 
at both the corresponding notes in the score — no matter 
whether looking at both is possible or, because of their 
distance apart in the score, impossible. He begins by 
looking at one of the notes, seeing, let us say, the 
other one in indirect vision and therefore indistinctly. 
He reacts to the former by a perfectly definite finger stroke. 
But the other note, not clearly separated from its sur- 
roundings by the perceiving eye, calls forth an incorrect 
or insufficient movement. The child tries again, and now, 
of course, looks at the note whose movement was not 
properly executed. Everything is reversed. The finger 
movement which was previously done badly is now done 
well, and the movement which was previously done well 

110 



SENSORY CONDENSATION 



111 



is done badly. After many trials, on the whole alternating 
as to the note favored by the eye, and as to the finger 
crowned by success, the child becomes able to perform both 
movements simultaneously with equal definiteness although 
he is looking at only one of the notes — no matter which one 
he is looking at. How do we explain this process of 
sensory condensation ? 

In order to explain it we make use of a diagram very 
similar to that of Figure 28, which helped us to explain the 
simple variation of a child learning to avoid contact with 
fire. For simplicity's sake, we represent the stimulation by 
the note looked at as a single strong nervous process 
taking its origin from S b (in Figure 34), and the stimulation 



Musical 
NoteJT 
5b> 



Musical 

Note I 




-M 

"RngcrU ™b M a Finger i 

Fig. 34 — Sensory condensation explained, 
by the note seen indirectly as a single weak nervous 
process taking its origin from S a . We learned from Figure 
28 that the motor response to this double stimulation, 
strong at S b and weak at S a , occurs only at M b - In 
the child's second trial everything is reversed. The 
stronger process is the one starting from S a and the weaker 
the one starting from S b > so that the motor response 
occurs only at M a . This goes on, the motor response 
occurring alternately at M b and M a . The question 
is what kind of changes the resistances of the various 
neurons undergo. 



112 HUMAN BEHAVIOR 

Plainly, when S a and S b are stimulated for the first time 
simultaneously and the motor response occurs at the 
point M h (see Figure 28), the neurons S 2 ab M 2 ab and M 2 ah Ml 
suffer a slightly greater reduction of their resistances 
than in case S b is stimulated alone. But it does not make 
any difference to the reduction of the resistance of the 
neuron S\M &, whether S b is stimulated alone or S a too. 
The flux from S b divides at the point S\ and goes on to 
M I partly over the direct, partly over the indirect route. 
Let us assume for the present, quite arbitrarily (we shall 
soon discuss this assumption separately), that the relative 
resistance of each of the four neurons S b Ml, S b Sl b , S 2 b M 2 b , 
M 2 ab M\ in case the flux comes exclusively from the sensory 
point S b , remains absolutely constant, so that none of 
these neurons is then in any respect favorably influenced, 
compared with the other three. When, however, S a is 
stimulated at the same time with S b , two of these four 
neurons are, with respect to the reduction of their resis- 
tances in consequence of their positive susceptibility 
undoubtedly in a more favorable position than the other 
two. The favored ones, S 2 ab M 2 ab and M 2 ab M\, in 
which occurs the additional flux deflected from the reflex 
arch S a M a , are marked in Figure 34 by a zigzag line. 
Soon, as we have seen in our example of the piano-playing 
child, the reverse stimulation occurs. S a is now stimula- 
ted strongly, S b at the same time more weakly. Of the 
four neurons S\M l „ S l a S 2 ab , S 2 b M 2 ab , and M 2 ab M\, two 
are now with respect to the reduction of their resis- 
tance specially favored, namely Sl b Ml b and M 2 ab M\. 
They are marked in Figure 34 in the same way by a zigzag 
line. If these two events happen alternately (this is 
the important condition, without which the outcome 
would be a mere variation of response) in a sufficient 
number of repetitions, the final result can be read off 



LOW AND HIGH CENTERS 113 

from the diagram of Figure 34. The relative resistances 
will be gradually changed so that ultimately any flux 
starting from either S a or S b exclusively, will take, in the 
main, the path over S 2 ab M 2 ab , divide at the point M 2 b almost 
equally, and cause a response at M a as well as at M b (a 
striking of both the piano keys), — practically as if neither 
the neuron S\M I nor S b Ml were any longer in existence. 
Thus this kind of a variation of the nervous path — sen- 
sory condensation — would have been explained, but only 
under the assumption just made that the relative resistance 
of any higher nerve center connecting the same correspond- 
ing points (for example S b and M b ) as any lower nerve center 
remains constant, however much the absolute resistance 
of all these centers may be reduced by a continuation 
or repetition of an isolated stimulation of the sensory point 
in question. This is the same assumption, only generalized, 
which we made with regard to four special neurons, 
and upon which we based our reasoning in the explanation 
of sensory condensation. This assumption is by no 
means self-evident. On the contrary, one might expect 
something very different. If S b alone is stimulated, 
the flux in the neuron S b Ml must be about three times 
as strong as in any of the neurons S&S^,, S 2 ab M 2 ab , and 
M 2 ab M\, since the path from S\ to M\ over these three 
neurons in series offers a greater resistance than the 
direct path over the single neuron S\M\. In conse- 
quence of the greater flux, the resistance of the neuron 
S\M\ might be expected to be reduced, by and by, 
relatively much more than the total resistance of the 
other three neurons is reduced. 

This last consequence, however, is biologically impossible. 
It would mean, in this special case, that the resistance 
of the neuron $\M b would tend to become so much 
reduced in comparison with any other nervous connection 



114 HUMAN BEHAVIOR 

between the points S\ and M\, that the reflex arch 
would be practically separated from its connection with 
the points S 2 b and M 2 ah . In general terms it would 
mean that all the reflex arches tend to become functionally 
separated from the higher nerve centers. Why 
should any animal have higher nerve centers, if the 
natural tendency of any nervous function from the 
beginning of individual life were to make the conduction 
of excitations over any higher centers more and more 
difficult and even impossible? The animal, then, might 
just as well, from the beginning of its life, possess no 
nervous conductors whatsoever, other than the reflex 
arches. It is clear, then, that we have, on quite general 
biological grounds, the right to assume that the relative 
resistance of any higher nerve centre connecting the same 
corresponding points as any lower nerve centre, in the 
case of isolated stimulation of the sensory point, remains 
constant. That is, in our special case (Figure 34), we 
have the right to assume, as we did, that when S b alone 
has been stimulated, and the flux has occurred, in accor- 
dance with the length of the conductors, more strongly 
over S b and M\ directly, more weakly over S 2 ab and M 2 by 
the ratio of the resistances of any two of the four connec- 
ting neurons involved always remains identical. Only 
simultaneous stimulation of a second sensory point can 
bring about a change of the relative resistances, — favoring 
the one or the other according to the special circumstances 
of the case. Our explanation of this case of sensory 
condensation is therefore complete. 

The assumption made concerning higher and lower cen- 
ters, which we found necessary on general biological 
grounds, may be stated also in different words. If the 
low r er nerve center (take as an example the connecting 
neuron S b M b in Figure 34) does not, in spite of the 



RELATIVE SUSCEPTIBILITY 115 

greater flux within it, suffer any greater reduction of its 
resistance than the higher center (SlS^M^Ml) 9 the 
positive susceptibility of the lower center is obviously 
less than the positive susceptibility of the higher center. 

If this holds good for the positive susceptibility, we 
have reason to ask if it applies also to the negative suscep- 
tibility. That it does, seems to follow from the familiar 
fact that any ability is lost through the normal process 
of forgetting the less readily, the greater the number of 
instinctive, low-centered relations contained in it. For 
example, we forget how to recite historical dates more 
easily than we forget how to skate. Perhaps, then, we 
are justified in stating the assumption quite generally 
thus: The neurons of higher centers have a greater suscep- 
tibility than those of lower centers. 

We have still to explain the third kind of variation 
of the nervous path, — that kind which we called motor 
condensation. The condensation of the motor activity 
can be explained in practically the same way as a variation 
of response. We have learned from Figure 28 that, when 
S a is rarely stimulated alone, but frequently together 
with S b and then less strongly than S b , the path leading 
from S a to M b tends to offer less and less resistance 
and finally to surpass greatly in conductivity the path 
from S a to M a . It is plain that when this stage of devel- 
opment has been reached, simultaneous stimulation 
of S a and S b can scarcely under any condition of relative 
intensity result in a simultaneous response at both 
the motor points M a and M b > but exclusively in a re- 
sponse at M b . 

But not all cases of learning which deserve the name of 
motor condensation are so simple. Let us take as a concrete 
and not too complicated example the baby who, during 
several months, can grasp small articles only by closing 



116 HUMAN BEHAVIOR 

his whole hand, but afterwards learns to grasp- a small 
article, for example a shirt button, between his thumb 
and index finger, like a grown person. At the sight of a 
sufficiently conspicuous object the young baby stretches 
out his arm. As a consequence of this reflex movement 
the fingers are stimulated by contact with the object. 
When the tip or any other part of the inner surface 
(from the nail toward the palm of the hand) of any finger 
is stimulated by touch, the finger reflexly bends. After 
a few months the baby learns to respond to the mere 
sight of an object by the initial part of the movement 
of closing the hand; that is, the fingers begin to bend while 
the arm is still being stretched out, before they have 
had any contact with the object. What gives, at this 
stage, the grasping a particular appearance of clumsiness 
is the fact that the thumb does not aid in grasping, but is 
left practically functionless. To understand this is not 
difficult if we recall the statement just made that the 
original (reflex) bending of any finger results from 
touch stimulation of its inner surface. When the arm is 
stretched out and the hand naturally drops on the object 
presented, the thumb is not stimulated, as the other four 




Fig. 35 — Thumb and finger movement, 
fingers are, on its inner surface, but on its side. This 
is the natural consequence of the anatomical location of 
the thumb, which moves, as the arrow in Figure 35 indi- 
cates, in the plane vertical to the plane of movement of 
the other fingers. Accordingly, the thumb has a less 
strong tendency to bend reflexly and, after the other fingers 
have bent, is prevented by them from bending. 



MOTOR CONDENSATION 117 

Compare with this clumsy manner of grasping the 
skill which the same child shows less than a year later, 
in taking hold of a small object. While the arm is being 
stretched out, in response to the sight of the thing, the 
thumb and the index finger assume positions opposite 
each other, ready to take the object between them. The 
other three fingers remain all the time at rest, in whatever 
position they happened to be at the start. If the object 
is of medium size, the middle finger assists the index 
finger. Only if the object is large, do all the four fingers 
come into action. In any case the thumb assumes a 
position opposite the fingers while the hand is still approach- 
ing the object, that is, in response to the mere sight of 
the object. 

This whole process of learning can be made clear by 
the aid of a comparatively simple diagram. S a represents, 
in Figure 36, the eye. The neurons S]M\ and M 2 ah M\ 
leading toward the motor organ which stretches the index 
finger, are marked as not yet developed. The shortest 
motor outlet from S a is therefore M b , the motor organ 
stretching the arm. In consequence of this stretch- 
ing of the arm, the points S d , S e , Sf, and S g , representing 
the finger tips, are stimulated. The reflex response at 
M d , M e , Mf, and M g is a bending of the four fingers and 
enclosing the object by them. The nervous processes 
from S d , S e , Sf, and S g attract, by dint of their own 
intensity, the process coming from S a and force it to 
take largely the path over S 2 ah Sl bcdefg Ml hcde f g M 2 cdefg and 
thence into M d , M e , M f , and M g . The resistance of 
this path decreases until, after repeated occurrence of 
this deflection and the fixation of the path, the excitation 
caused at some time at S a travels in the direction of 
M d , M e , M}, and M g and causes the beginning of a bending 
even before any of the finger tips have been touched. 



IIS 



HUMAN BEHAVIOR 



Oabcdefg 



I abcdefg 




S a M a M b SgSfSeSdSc M c M d M e Mf M g 

lug. 3(5 — Learning how to grasp. 

Sa, Eye— Ma, Stretching index finger — Mb, Stretching arm — S c , 
Tip of thumb— S d, Tip of index finger— M c , Bending thumb— Md, 
Bending index finger — Zigzag, Neurons undeveloped at birth. 

This accomplishment becomes the subject of a new 
influence at some time during the second half of the first 
year. The neurons marked in Figure 36 by zigzag lines 
reach by this time their full development and establish 
a new hereditary connection. When now the eye is 
stimulated, not only the arm but also the index finger is 
stretched out. This reflex appears at about the same time 
that the first articulated sounds (usually dental and 
guttural — "da" and "ga") are instinctively enounced by 
the baby, — a coincidence the significance of which we shall 
discuss at a later time. The result of this stretching of 
the index finger, with the other fingers in their ordinary 
slightly bent position, is touch stimulation of the tip 
of the index finger exclusively. Since the other fingers 
remain unstimulated, the index finger alone bends. If the 



GRASPING 119 

object is small, this bending movement of the index 
finger touching it is likely to pull the object toward the 
hand. When this is actually done, the object comes into 
contact with the outer surface of the other fingers and the in- 
ner surface of the thumb. The former contact is irrelevant, 
because it occurs on the outer surface; but the contact with 
the thumb is followed by a reflex bending of the thumb, 
so that the object is squeezed between the thumb and 
index finger. This means, in the diagram of Figure 36, that 
the two nervous processes from S c to M c and from S d to M d 
deflect the nervous process coming from S a by dint 
of their greater intensity and force it to take the path 
over Sri cdefg9 Ml bcdefg , and M 2 cdefg into M c and M d . If 
this whole occurrence happens repeatedly, the resis- 
tance of the path from S a into M c and into M d is 
so much lowered that finally, at the appearance 
of the object, the excitation travels not only to 
M a and to M b , but largely also to M c and M d and causes 
a motor response here too, although slightly later than 
at M a and M b because of the difference of the distance. 
This makes it plain, why toward the end of the first year 
the child responds to the mere sight of an object by 
stretching out his arm and at the same time making 
the thumb and index finger ready to receive the 
thing which has been presented to the eye. The 
motor expansion, the clumsy use of the whole hand, has 
been succeeded by the motor condensation, the use 
of two fingers only. 



TENTH LECTURE 

Order of acquisition of the first four classes of habits. 
Control of the sense organs of the head. Direction and 
extent of the fixation movement of the eye. Improvement by 
experience of the fixation movement of the eye. A variation 
of response resulting from a close succession of nervous 
processes just as from a deflection of one by another. Co- 
ordination of the eyes. How an infant learns to face a 
sounding object. Control of the hands and arms. Learning 
to raise the arm in response to a visual object above the eyes. 
Loose co-ordination of eye and hand. 

WE have considered the change of behavior, 
which we call learning, in its positive as 
well as in its negative aspect. We have 
recognized that learning and unlearning 
(inhibition) are only the positive and the negative aspect 
of the same nervous function. We have further convinced 
ourselves that the three classes of change of behavior, 
which seem to include all possible kinds, variation of 
response, sensory condensation, and motor condensation, 
are at bottom the same nervous function, which in its 
simplest form we have called variation of response. The 
above explanation of this nervous function, however, is 
applicable only in case one nervous process which influen- 
ces another, begins before the other has ceased, that is, in 
case of simultaneity. Learning as applied to successive 
nervous processes will be explained farther below. We shall 

120 



FIRST HABITS 121 

first make ourselves acquainted with the most fundamental 
reflex activities of childhood from which human learning 
develops. The study of this development will show us 
in what respects the explanations of human behavior 
given thus far are sufficient and in what respects they 
need to be supplemented. 

Childhood is the very age of learning in human life. 
Great as the accomplishments of human beings may 
appear which are acquired in schools and colleges, they 
are as a matter of fact small when compared with those 
of the first six or seven years, before the individual is 
systematically trained by his teachers. It is of the utmost 
importance for the teacher to understand how learning 
proceeds before it is systematically directed, in order to 
avoid the forcing of the individual into an educational 
system which is unrelated — or even opposed — to the 
natural way in which man acquires his habits in early 
childhood. The first habits acquired by the baby are 
those connected with the use of the sense organs of the 
head. Then the baby learns to use his arms and hands. 
Toward the end of the first year or soon thereafter he 
learns to use his feet for walking and running, and toward 
the end of the second year to use his vocal organs for 
speech. Of course, we do not mean that each one of these 
classes of activities must become perfect before the next 
begins, but merely that they usually become conspicuous 
in this order. Besides, it is well to keep in mind that 
individual differences are exceedingly common, so that 
these four stages of development are not in every child 
equally obvious. 

Of the sense organs of the head, the eyes are those whose 
efficient use depends most on proper motor adjustments, 
— much more so than the ears or the sense organs of the 
mouth. The chief reflex of the eye consists in a turning of 



122 HUMAN BEHAVIOR 

the center of the eye, the "fovea," the area of most 
distinct vision, in the direction of the most effective 
object of visual stimulation, in a "movement of fixation" 
as we may call it. It is quite natural that this response 
at first is often rather inadequate in accuracy of direction 
and particularly of extent, — the center of the eye moves 
either beyond the point where it could receive the optical 
rays from the object in question or not far enough to 
reach this point. Gradually, however, the movement 
becomes more and more adequate. Yet it never becomes 
absolutely exact even in adult life. Even the grown 
person, in order to fixate an object, must, practically 
without exception, correct the first sweeping movement 
of fixation by smaller ones before a sufficiently accurate 
adjustment of the fovea is obtained. Figure 37 gives an 
example of a complex eye movement of this kind, the 
first sweep of the object's image being from S a to S b . 




Fig. 37 — Fixation movement of the eye. 
On Retina: F, Fovea — Sa, Point stimulated before fixation movement — 

Sb 9 Point stimulated after fixation movement. 
On Field of Vision: F, Point to be fixated— Sa, Point fixated before 

movement — Sb, Point fixated after movement. 

Two things need explanation. First: why the eye ball 
moves always in the direction of the stimulus. Secondly: 
why the eye ball stops at the moment when the fovea is 
approximately opposite the stimulus. The first is easily 
explained. The various sensory points of the retina are 
doubtless connected with the eye muscles by reflex arches 
in such a way that, when any point of the retina is especial- 
ly stimulated, the excitation takes its path toward those 
muscles or groups of muscles which pull the eye in the 



EXTENT OF EYE MOVEMENT 123 

proper direction. In this respect no learning is necessary. 
The direction is determined reflexly. The second question 
is less easily answered. Why does the eye movement stop 
as soon as the fovea has approximately reached a point 
opposite the object? One feels inclined to think that 
during the fixation movement of the eye the object, 
suddenly striking with its rays the fovea, sets up there a 
particularly effective excitation which either results reflexly 
in a muscular contraction capable of fixing the eye in 
the position just reached, or stops the movement by 
inhibiting the nervous process which causes it. Such 
explanations could still be offered as recently as ten years 
ago. But the research of the most recent years has dis- 
credited them. For some reason or other sensory excita- 
tions received while the eye moves, fail to become effective 
and, therefore, can not in any way stop the movement. 
The extent of the sweeping movement of the eye must also 
be determined reflexly and in advance of the motion — 
probably by a strong excitation reaching the muscles which 
pull the fovea in the proper direction and a relatively 
weak excitation reaching the antagonistic muscles. If the 
inherited connections of every point of the retina with 
the various groups of muscles are such as to determine 
through their resistances a definite ratio of the two anta- 
gonistic muscular effects just mentioned, the eye must 
clearly stop at a definite point, — where the antagonistic 
motor effects balance each other. Figure 38, for clearness ' 
sake, suggests how the nervous conductors might be 
arranged in order to bring about this result; but we do 
not, of course, assert that they are arranged just in this 
way. The figure contains only two motor points, M L and 
Mr, representing, say, the muscles which pull the eye to 
the left and those which pull to the right. The sensory 
points represent a series from one side of the retina, at 



124 



HUMAN BEHAVIOR 




\ ^L ^L °L °L ^L ^R ^R U R ^R ^R 
Fig. 38 — Simultaneous innervation of antagonistic muscles. 

S'l, (the right side, opposite the left edge of the field 
of vision) to the other side, at S R '. It is evident that a 
nervous process starting, for example, from S L must go 
mainly to M L , traveling thus over the smallest number of 
neurons possible; but a considerable fraction of it must 
pass over S^rM^r to M R . A nervous process starting, 
for comparison, from S' L can send only a smaller part of 
its total flux to M L , since the resistance of the path from 
S' L to M L is greater than that of the path of fewer neurons 
from Sl to M L : so a larger fraction of the flux takes the 
now shorter path over S\rM 1 L r to M R . The farther we go 
to the sensory points at the right of the figure, the more 
we find Mr favored in comparison with M L . Thus the eye 
must come to a standstill at different angles according to 
the sensory point excited and the corresponding ratio of 
the excitation of the antagonistic muscle groups. 

This is simple enough thus far. However, this ratio 
does not seem to be established by inheritance with any 
great exactness, so that there is still left the problem which 
is of special interest to us in this study, namely, how we 
can explain the great improvement in the accuracy of the 
fixation movement which is to be observed during the 
first weeks and months of life, — how the child learns to 
execute these sweeping fixation movements with so much 
more accuracy in direction and extent after a few months 



IMPROVEMENT OF EYE MOVEMENT 125 

of experience. The very purpose of our present study is, 
not to take learning as a phenomenon which is too common 
to need explanation, but to arouse our curiosity about it 
and to satisfy this by making the process of learning as 
plain as the running of a steam locomotive. 

We may restrict our discussion to the extent of the 
movement stopping at, or before, or beyond a certain 
point, but always on the straight line passing through it. 
A movement along a line leaving the point to be fixated 
more or less at one side, is obviously simply the com- 
ponent, geometrically, of two movements, two muscular 
effects, and does not involve any additional principle of 
explanation. We shall, then, have to solve the following 
typical problem: If in earliest childhood, the fixation 
movement brings the image, let us say, from S a , in Figure 
37, to S b , some distance beyond the fovea, why is it that 
after some experience the sweep is so much shorter that 
the image is brought from S a to the nearest neighborhood 
of the fovea? 

Figure 39 will aid us in understanding how the fixation 
movement of the eye can be improved by experience — 
in understanding, at the same time, what the often mys- 
terious word "experience" really signifies. S a represents 
the sensory point where the image of the object first 
appears on the retina, M a the motor point which signifies 
pulling the fovea in the direction of the optical image. 
M b represents the motor point which signifies pulling the 
fovea in exactly the opposite direction. In order to bring 
about the proper movement of approximately the right 
extent, both M a and M b must be excited, — but M a more 
strongly (if equally, there would be no movement at all), 
M b only strongly enough to bring the eye ball after some 
time to a standstill, through the balancing of the opposite 
forces of muscular tension. The antagonistic muscles. 



126 



HUMAN BEHAVIOR 



fa such a case, must act upon the eye ball in the same way 
in which two rubber bands of different tension, attached 
to and pulling, say, a piece of cork in opposite directions, 
would act. We have assumed that the tension resulting 
from|2f a is relatively too great, so that the image, instead 
of falling upon the fovea, now falls at a point S b , some- 
what beyond the fovea. It is easy to understand from 




■a f% S5 

Fig. 39— Improvement of the fixation movement of the eye. 



Ill 



Figure 39 why stimulation of S a should result in a stronger 
excitation at M a and a weaker one at M b . But why 
should, at a later recurrence of the stimulation of S a , 
after the "experience" has become effective, the excita- 
tion at M b be relatively greater, thus balancing the effect 
of M a sooner and preventing the fovea from moving as 
far as the first time, stopping it nearer the correct point 
of fixation, the point F in Figure 37? The answer to this 
question is the solution of our problem. 



THE CORRECTING MOVEMENT 127 

In order to give the answer, we must consider the 
correcting movement. As soon as the eye stops after 
having swept too far, S b is stimulated by the new optical 
impression, and — everything being exactly reversed — 
the fovea is pulled in the opposite direction. Let us see 
what neurons conduct the excitation whenever S b is 
stimulated. They are, eight in number, marked in Figure 
39 partly as broad, partly as double lines. A moment 
ago S a was stimulated and the excitation took its path 
over some of these very neurons, namely, over those 
drawn in broad lines. The effect of that excitation, 
reducing the resistance of the neurons, lasts for some 
time before the negative susceptibility begins to restore 
the former resistance, as discussed previously and illus- 
trated in Figure 33. Therefore, when now S b is stimulated 
and the excitation coming from S b reduces the resistance 
in all the neurons through which it passes, the resistance 
jf the neurons drawn in broad lines not merely begins to be 
reduced, like the resistance of the neurons drawn in 
double lines, but is further reduced. In the total system of 
Figure 39, the neurons drawn in broad lines thus suffer a 
relatively greater reduction of their conductivity than all the 
others. It is easy to see that our problem is herewith 
solved, for when now at any time the retinal point S a 
is again struck by an optical image, a greater fraction 
than originally of the excitation from S a can pass over 
SabM ab and M^Ml into the non-corresponding point 
M bi causing a stronger muscular tension at M b and an 
earlier balancing of the antagonistic forces which bring 
about the sweeping movement of fixation. 

To remove all doubt as to the correctness of this con- 
clusion let us look again at the broad lines of Figure 39. 
The short route from S a to M a consists of three neurons, 
of which one is favored by the effect in question; that is, only 



128 HUMAN BEHAVIOR 

one-third of the total length of the path. The longer route 
from S a to M a and the route from S a to M b , however, 
consist each of five neurons, of which three are favored 
by the effect in question; that is, as much as three-fifths 
of the path. It is clear that the total result of this widen- 
ing of one-third of the length of one path and of three- 
fifths of the length of the other path is to the advantage 
of M b , to the disadvantage of M a . The ordinary superiori- 
ty in intensity of response (to stimulation of S a ) of M a 
over M b is based on the greater conductivity of the reflex 
arch S a S l a M l a M a , which has now been relatively diminished. 
Any relatively greater reduction of the resistance of the 
higher center S 2 ah M 2 ah must favor the ordinarily quite 
weak response of the non-corresponding point M b , to the 
disadvantage of the corresponding point M a . The motor 
effect of M b now balances the effect of M a a little earlier, 
brings about the stopping of the eye movement a little 
earlier. That is, the next fixation movement is more 
correct. 

We see, then, that the improvement of any particular 
nervous function by "experience" of the individual is an 
altogether natural phenomenon, — no more mysterious, 
although different in kind, than the gradual improvement 
of the draft in a cold chimney after the fire has been 
burning for some time. A few fundamental laws which 
we assume as governing nervous activity are sufficient 
to explain this learning by experience, without any 
necessary reference to "conscious" experience. The 
present case is clearly a variation of response, for we have 
now a relatively strong motor effect where (at M b in 
response to a stimulation of *S a ) we had originally only a 
weak part of the total effect. But we notice the important 
fact that the variation has come about without a deflection 
of one nervous process by a simultaneous one taking 



VARIATION BY SUCCESSION 129 

place. We see, then, that the same variation which can 
be the result of a deflection, can also be the consequence 
of a succession of nervous processes, provided the law 
illustrated in Figure 33 is applicable, the law that any 
reduction in resistance remains for a short time (a few 
seconds at least) uninfluenced by the negative susceptibili- 

ty. 

We have explained how the improvement of the accur- 
acy of the fixation movement comes about, which dimin- 
ishes the need for movements of correction succeeding 
the first sweep. Simultaneously another improvement 
takes place, — that of the co-operation of the two eyes. 
During the first days of a baby's life it may not infre- 
quently be observed that the eyes move independently 
of each other, that one moves to the right while the other 
stands still or moves even to the left. This is but natural 
since a striking object may not impress one eye as strongly 
as the other, indeed may be invisible to one eye if it 
happens to be near the right or left edge of the total field 
of vision. How, then, is the nervous system "educated" 
so that later both eyes always move together to the right 
or left, even when the object is, in advance of the move- 
ment, invisible to one eye? 

In Figure 40, M t and M r represent those motor points 
whose simultaneous excitations cause the simultaneous 
and similar movements of the two eyes. Whenever S t 
and S r are stimulated simultaneously and with equal 
intensity, as it happens most frequently, the simultaneous 
excitations of the two motor points are self-evident. 
But why are, after a few months of life of the individual, 
the motor points simultaneously excited even when one 
of the sensory points is unstimulated? This is clearly a 
case of sensory condensation. It may be thought to come 
about in the following way. 



130 



HUMAN BEHAVIOR 



Whenever Si is stimulated alone, by far the largest 
part of the excitation takes its path over the reflex arch 
directly to M t . A smaller, though" considerable, part, 
however, takes the indirect path over S?Mf and even 
over Sf r Mf n mostly in the direction of M h but to some 
extent also in other directions, for example, toward M r . 




^ Mi 

Left Eye 



S r M r 

Right Eye 



Fig. 40 — Co-ordination of the two eyes or any two organs. 

Whenever S r is stimulated alone, by far the largest part 
of the excitation takes its path over the reflex arch directly 
to M r . A smaller, though considerable, part, however, 
takes the indirect path over S^M'f and even over Sf r M%, 
mostly in the direction of M r , but to some extent also 
in other directions, for example, toward M t . In either 
case, when S t or S f is stimulated alone, the relative resist- 
ance of the lower and higher neurons involved remains 
unchanged, in accordance with the law which we assumed 
in the preceding lecture. But when Si and S r are stimu- 



CO-ORDINATION OF THE EYES 131 

lated at the same time, those neurons which belong to the 
system of S c as well as to that of S r are favored over all 
the others with respect to the reduction of their resistance, 
since a double excitation — and therefore a stronger flux — 
passes through them. These neurons are drawn in Figure 
40 in double lines. The relatively greater reduction of 
the resistance of these neurons may amount to but little 
in a single case of "experience." But it must become 
quite considerable in a few months, since simultaneous 
stimulation of both eyes by the same object is naturally 
a very common occurrence. When the resistance of the 
double drawn neurons has become much reduced, an ever 
increasing amount of the flux takes its path, instead of 
over a reflex arch, over the higher center Si r Mf n which 
forms the connecting bridge between the two eyes. Ac- 
cordingly, an ever increasing part of the flux finds its way 
from M\ down into M r even when Si happens to be 
stimulated alone, or into M t when S r happens to be 
stimulated alone, until finally the response occurs regularly 
at both M t and M r no matter whether both the sensory 
points are stimulated or only one of them. That is, the 
movements of the eyes have become perfectly co-ordinated. 
The co-ordination of the eyes is an example of that 
kind of variation of the nervous path which we have called 
sensory condensation. Another example of sensory con- 
densation which we have studied in detail is that of a child 
learning to execute, on the piano keyboard, two finger 
movements in response to only one note. The explanation 
in detail of the two examples is somewhat different owing 
to the fact that in the former case the sensory condensa- 
tion results from a two-fold stimulation of unequal intensi- 
ties, the one and the other sensory point being alternately 
more strongly excited, whereas in the present case both 
sensory points are usually stimulated with the same 



182 HUMAN BEHAVIOR 

intensity. We have thus seen that sensory condensation 
can result under various circumstances, provided only 
that the reflex arches involved are connected — and not 
too remotely — by higher nerve centers. 

Xext to the eye, the ear is the sense organ of the head 
which is most interesting because of its motor adjustments. 
We are naturally inclined to assume that there is here a 
reflex similar to the turning reflex of the eye, — that, when 
a sound strikes one of the ears more strongly than the 
other, the face turns reflexly toward the source of sound. 
This would mean that, by inheritance, of the muscles 
turning the head those on either side are more closely 
connected with the one ear than with the other ear. The 
purpose of this head movement would be, not so much a 
better adjustment of the organ of hearing, as of the organ 
of sight, — the eyes when facing the source of sound would 
be more likely to receive from it an effective visual stimu- 
lation. Such a reflex response, however, a turning of the 
face in the direction of a sound, does not seem to exist. 
When a child is five to six months old, this response is 
quite common, but during the first three months it does 
not occur. One may, of course, assume that the reflex 
does not mature until several months after birth, and 
support this assumption by the fact that some instincts 
and reflexes mature even years after birth. However, 
reflexes whose maturity is undoubtedly delayed — take 
for example the sexual — are obviously delayed because 
their appearance directly after birth would be useless. 
But turning the head in the direction of a sound would not 
be entirely useless even in earliest infancy. We may 
therefore, as long as the question is left undecided by the 
physiologists and anatomists, regard it as most probable 
that the turning of the face in the direction of a sound is 
not a reflex, but a habit which is usually established three 



LEARNING TO FACE A SOUND 133 

or four months after birth. Our problem, then, is to 
explain how the individual learns to respond thus to 
sounds which stimulate the two ears unequally. 

There can hardly be any doubt that the habit of turning 
the face toward a source of sound is a variation of response 
— one of that kind in which the same response occurs, but 
another stimulus has been substituted for the original one. 
The original stimulus is visual. The fixation reflex of the 
eyes can be observed as functioning a few weeks after 
birth; and the reflex turning of the head can be seen to 
support and supplement the eye movement at the same 
early age, — in response to sight, for reflex movements of 
the head in response to tactual stimuli occur even a few 
days after birth, when the baby, held to the mother's 
breast, hunts, so to speak, for the nipple. Objects which 
appear in indirect vision and therefore call forth the 
fixation reflex, are frequently sources of sound, — for 
example, the mother's face. That is, the baby's ears 
are stimulated at the same time as the eyes. If the 
nervous flux coming from the ear more strongly stimulated, 
and including, by deflection, most of the flux from the 
other ear, has no particular reflex outlet, it must take its 
path, other things being equal, mostly in the direction of 
any other strong nervous process existing at the same time 
and therefore attracting it. It must take its path in the 
direction of that motor point which in response to the 
visual stimulation turns the head to face the source of 
sound. There is no danger that the reverse might occur, 
that the nervous flux coming from the eye might be 
attracted by the flux from the ear, for we are working 
under the assumption that the flux from the ear has no 
low-resistance reflex outlet and, therefore, cannot attain 
any such great intensity as that from the eye. When the 
deflection from the ear to the head-turning muscles has 



184 HUMAN BEHAVIOR 

occurred often enough and the resistance along this path 
has been effectively lowered, the habit which we intended 
to explain is established. The head then turns even in 
response to a source of sound which may remain perma- 
nently invisible. That the habit is not established until 
several months after birth, is caused probably by the 
absence, at an earlier time, of connecting neurons which 
are capable of serving as a chain of conductors. It is a 
well established fact that the majority of the higher nerve 
centers capable of serving such remote connections are 
immature at birth and fairly mature only three months 
later. 

The next large group of activities we proposed to study 
are those of the hands and arms. We have already seen 
how, from the reflex of a bending of the fingers in response 
to a stimulation of their inner surfaces, the delicate and 
skillful grasping of the older child and of the adult develops. 
We have also mentioned that the arm is reflexly stretched 
out in response to a stimulation of the eye. With respect 
to the arms, there are several further details which are 
interesting enough to be mentioned here. 




Fig. 41 — liaising the hand. 

With an adult, the raising of the hand in response to 
sight, as when we take a book from a shelf above our head 
(Figure 41), is a very common movement. During the 



BABIES AND APES 135 

first months a similar response to sight, moving the hand 
in the direction from the feet to the head, does not occur. 
The movements — like many, other properties — of a human 
baby have often been compared with those of full-grown 
animals, for example, the apes; and, since the apes are 
climbers, one might conclude that the movement of Figure 
41, which is common in climbing, must be frequently 
observed in babies. We see here, that, as a matter of fact, 
one has to be very critical in such comparisons. The apes 
are indeed climbing animals and, as such, are compelled 
to execute the arm movement in question quite frequently; 
but only in adult life, — the baby apes do not climb any 
more than human babies, but cling to their mothers who 
carry them about. The comparison is therefore not 
really between babies and apes, but only between human 
babies and monkey babies. When the very young baby 
stretches out his arms, in response to a visual impression, 
it is always either at right angles to the longitudinal 
axis of the body or more downwards, toward the feet, 
never more upwards, toward the head. The same is 
probably true for the monkey baby. 

How, then, does the baby learn to raise his hands in 
response to a visual stimulation? In order to answer 
this question, we must inquire whether there is during 
the first few months any reflex raising of the hands, and 
whether there is any possibility of this reflex being varied so 
that a visual stimulation takes the place of the stimulation 
of this reflex. There is a reflex of throwing up the arms, 
namely, in response to the application of cold to the skin 
of the body During the first days the new-born baby is — 
however strange this may seem — rather insensitive to all 
stimuli applied to the £kin, be they heat or cold or pressure 
or the prick of a needle. But after the third week, if the 
baby is suddenly uncovered and exposed to a draft of cold 



136 HUMAN BEHAVIOR 

air, or placed on a cold linen cloth, or immersed in cool 
water, he may be seen to throw up his arms violently. 

How, then, can these upward movements of the arms 
become associated, so to speak, with visual impressions? 
Incidentally the hands, during the upward movement, 
impress themselves as visual images upon the eyes, — 
upon the lower parts of the retinas, since all rays are 
crossed at the entrance to the eye. While the nervous 
process of the above mentioned reflex goes on, another 
nervous process thus starts from the lower region of the 
retina. The latter may be assumed to be especially 
intensive because it is caused by an object in motion. 
Although it is not perfectly known how this is brought 
about, it is a perfectly familiar fact that on the peripheral 
parts of the retina an object in motion produces a specially 
effective nervous process, much more effective than those 
resulting from the impressions of motionless objects. It 
therefore draws all the other visual nervous processes 
into its own channel and is the only visual nervous process 
which w r e have to take into account. The reflex motor 
effect of this process is probably a turning of the eye 
upwards. A considerable part of this visual nervous 
process is now likely to be deflected from its course by the 
other nervous process, still going on, into the direction 
of the motor organs which served the violent throwing up 
of the arms. Accordingly the resistance of the path lead- 
ing over higher nerve centers from the lower part of the 
retina to the muscles raising the arm is reduced; and when 
this reduction of the resistance of the path has become 
sufficiently great, the hand will be stretched upwards in 
response to a visual stimulus coming from an object in 
front of the head and more or less above the eyes — a 
reaction which is quite common in the half-year old 
child. This variation of the nervous path is simply a 



HANDS AND EYES 137 

further example of that kind of a "variation of response" 
in which the same response is called forth by a new kind 
of stimulus. 

Of course, the establishment of an habitual upward 
movement of the hands in response to a visual stimulation 
does not necessarily interfere with the reflex of turning 
the eyes upwards in response to the same kind of stimula- 
tion. In order to establish the habit only a part of the 
nervous flux of the reflex need be deflected into the new 
motor outlet; and the final result may be a co-existence, a 
loose co-ordination of the two upward movements of the 
hands and the eyes. A similar loose co-ordination of 
eye and hand movements in a horizontal direction, to the 
right and left, can be observed in children as early as the 
third month. 



ELEVENTH LECTURE 

Control of the feet. The ability to walk equal to 
rising plus balancing. Reflex of straightening the leg. ■ 
Reflex of squatting. Balancing with hand support preceding 
free balancing. Balancing on one leg preceded by balancing 
on both. Walking not a simple instinct, but a compound of 
reflexes united largely by experience. Balancing sideways 
preceding balancing fore and aft. Stretching the foot 
reflexly toward a thing which impresses the eye. Locomo- 
tion resulting from this reflex. Creeping. Creeping on 
two legs preceded by creeping on one. Influences of 
creeping on walking. Sitting up. Finger-sucking super- 
ceded by other habits. Free standing rarely preceded by 
walking. One-sidedness and general clumsiness of first 
walking. Encouraging a child to stand: a purely negative 
event. The so-called instincts of constructiveness and 
destructiveness : rather habits. 

WHATEVER may be— practically and 
scientifically — the relative importance 
of arms and legs, hands and feet, the 
control of the feet, the acquisition of 
the ability of locomotion in the up-right position, 
lias always attracted the chief interest of the amateur 
observers of child life, the parents and nurses. When the 
child can walk, their interest in observation almost 
ceases. And yet, most animals possess the ability of 
locomotion practically from birth, so that, in this res- 

138 



WALKING 139 

pect, the year old child merely attains the level of a new- 
born animal. The control of the hands when once fully 
attained, places the child on a level which no animal 
ever reaches. Nevertheless, walking attracts more 
attention than the control of the hands, probably be- 
cause the change from the perfectly helpless condition 
of human infancy to an animal-like condition lessens 
the responsibility of the child's care-takers so much 
more suddenly than any of the changes which raise 
the child above the level of animal life. 

The complete ability of locomotion in the upright 
position involves two distinct abilities of muscular action : 
the ability to rise from a lying to a standing position and 
the ability to balance on either leg. The ability to rise 
is only imperfectly developed as long as holding on an 
object, a chair or the like, is necessary in order to rise. 
This imperfect ability usually precedes by several months 
the child's ability to rise to his feet from the floor without 
the aid of any supporting object. The ability to balance 
on (either) one leg is naturally preceded — as a rule — by the 
ability to balance on both legs, which, on the whole, is 
more easily acquired. 

The governing reflex of the whole group in ques- 
tion seems to be that of straightening the legs in 
response to pressure against the soles. A child about 
nine months old, or even considerably younger, 
may absolutely "refuse" to be held on anybody's arms 
in a sitting, flexible position. The reflex of straightening 
the legs causes a stiffening of the body. The mother then 
naturally places the child, no longer easily held in her arms 
when in this straight position, with his feet on her knees, 
or a table, or the floor. The child then stands, in a way, 
but retains this standing position only because he is 
kept from tumbling by his mother's arms. Soon the 



HO HUMAN BEHAVIOR 

child learns to use his own hands, in the control of which 
he has by this time already acquired considerable skill, 
in order to keep from tumbling. He grasps whatever is 
in sight and reach and thus learns to keep in a standing 
position. Another reflex reaction is soon added to those 
of grasping the things which are seen and of straight- 
ening the legs when the soles are touched: that of 
changing from a standing to a squatting position, in 
response — probably — to sensory excitations in the muscles 
and joints of the legs when supporting the body. The 
following periodic activity must then frequently take 
place. The child changes from a standing to a squatting 
position while having his mother's clothes or any other 
object in his grasp. Being in the squatting position he 
no longer receives the sensory excitations which caused 
squatting. Consequently the excitation of the soles of the 
feet regains its former relative power and straightening 
of the legs occurs. At the same time the touch of the 
objects in the child's hands causes a bending of the 
arms, an action derived perhaps from the reflex of put- 
ting things into the mouth, so that the whole action 
might be described by saying: the child gets up, pulling 
himself up by his hands. This may be followed again by 
squatting, again by raising himself, and so on. Since the 
squatting, when the body is held in the upright position 
by the hands having grasped an object, readily changes 
into kneeling, the periodic action may be: kneeling, stand- 
ing kneeling, standing, and so on. Further, when there 
arc solid objects which the hands can grasp, the body 
i- easily pulled up from a lying to a kneeling position, so 
that there may be a change from lying to standing, and the 
reverse, provided only that the grasping hands can come 
into play. 

When the child stands before an object, holding on with 
both hands, it naturally happens that now and then one 



FROM LYING TO STANDING 141 

of the hands loses its grasp. If this happens while his 
legs are perfectly straight, he is likely to tumble down 
toward the side of the other hand; and then he will get up 
again. But if it happens while the legs are in a slightly 
bent position, intermediate between standing and squat- 
ting, it means only that the weight of the body is thrown 
on one side and that the leg of this side is straightened 
in response to the increased pressure on the sole. Thus 
the body is again balanced and kept from tumbling. This 
ability to balance the body is then further improved in 
two ways. First, the resistance of the nervous path from 
the sensory points of the sole to the muscles straightening 
the leg is lessened, possibly by the mere maturing of the 
inherited reflex. Accordingly, sensory excitations of much 
smaller intensity, caused by much weaker pressure on 
the sole when the body is barely beginning to lose its 
balance, are capable of bringing about the motor res- 
ponse which restores the balance. Secondly, the nervous 
processes starting from the excitations of the sensory 
points in the muscles, tendons, and joints of both legs are, 
by motor condensation, caused to contribute to the motor 
response which restores the balance temporarily impaired. 
This second kind of improvement, when further developed 
in later years into an independent "variation of response", 
becomes our ability to stand on one leg and to balance 
our body on one leg in dancing or skating. When the 
child has had a certain amount of practise in retaining its 
upright position, both hands may lose their grasp on the 
supporting object without causing any tumbling. The 
equilibrium of the body is then at any time restored by 
the newly acquired motor responses as soon as it is lost. 
We say that the child has "learned" to stand alone. 

Let us return to the moment described in the beginning 
of the last paragraph. While the child is standing before 



142 II I'M AN BEHAVIOR 

an object, holding on with both hands, one of the hands 
loses its grasp and consequently the leg on the other side 
is straightened. The body as a whole, perhaps, is thus 
somewhat raised, and with it that leg which remained 
slightly bent. But now this leg, hanging and subject 
to the effect of gravity, straightens somewhat; and when 
the body regains its vertical position and the foot of this 
leg touches the ground, it straightens perfectly, owing 
to the reflex repeatedly mentioned. The weight of the 
body is thus thrown again — lightly — upon the other leg. A 
swinging movement of the body may thus result, from the 
left to the right, from the right to the left. It is clear that 
this movement needs only a slight modification to become 
a regular walking movement. Children who are just be- 
ginning to walk, do indeed, usually, walk in this pendulum- 
like fashion, comparable to the walking of a sailor. One 
finds here and there in psychological literature the asser- 
tion that the walking of a child is the result of an instinct 
consisting in a tendency of the legs to swing fore and back 
in directions opposite to each other, and that these instinc- 
tive movements can be observed in a baby a few months 
old when held suspended. While such opposite fore and 
back swinging movements of the legs may sometimes be 
observed, it seems doubtful if they have much significance 
for the acquisition of the ability to walk, since one does not 
walk in suspension, but on a supporting surface. In any 
case, it is possible to derive the alternate movements 
of the legs in walking from the reflex of straightening each 
leg in response to pressure against the sole, without assum- 
ing any specific "instinct of walking." 

We described how a child may learn to stand 
alone, balancing himself sideways. But in order 
to stand really alone he must also keep from losing 
his balance in the forward and backward directions. 



BATANCING 143 

From falling forward he may be kept by the very 
reflex of straightening mentioned before. When the 
body begins to move forward, less weight is placed 
on the heels and more on the soles. Accordingly the 
foot straightens, the heel is raised above the ground and 
the body is kept from moving forward since the centre of 
gravity is now behind the point of support. On the other 
hand, when the body begins to move backward, more and 
more weight is placed on the heels, the pressure on the 
soles vanishes, and the muscles which keep the legs straight 
relax. The knees then bend forward and thus a part of the 
weight of the body is thrown in front of the previous center 
of gravity, thus restoring the balance. Just as the swing- 
ing of the body to the left and right, so these kinds of 
movement have great significance for walking. In the 
walking movements of a grown person the raising of the 
heel of one foot may raise with the whole body the other 
foot from the floor and cause it by the mere force of 
gravity to swing forwards. 

We have been trying to explain how a child learns to 
balance its body in the upright position without having 
to hold to an object. Before this accomplishment of 
standing free, the child usually begins to walk along by 
pieces of furniture, changing the hold of his hands as he 
walks on. What reflex is the basis of this locomotion? 
It seems that, in response to a visual stimulation, not only 
the hand but the foot, too, stretches toward the thing 
which impresses the eye. On the basis of such a reflex 
locomotion is easily explained. Imagine a child standing 
before a bench, holding on with both hands, and an object, 
say, a pencil, lying on the end of the bench to the right. 
The effect of the stimulation of the eye by the pencil is 
a stretching of the right arm and the right leg to the right. 
The body then falls to the right until the right foot again 



144 HUMAN BEHAVIOR 

t ouches the ground. The body is now somewhat displaced 
to the right. The feet are farther apart than normally 
and are therefore, in consequence of special reflexes which 
we need not discuss, brought together to their normal 
position, but of course, without any essential change of 
the body sideways. Now the whole stretching of the 
right hand and the right foot to the right may be repeated 
several times, until the hand grasps the object. This 
walking along the pieces of furniture or the walls of a 
room can therefore be very simply explained. 

At about this time in a child's development another 
kind of locomotion is likely to make its appearance, — creep 
ing. As the baby happens to lie on his stomach, his eye is 
stimulated by an object and the arms are reflexly stretched 
forward, — but not the arms alone, the legs too are 
stretched, these backward, of course; and later a draw- 
ing in of all the extremities simultaneously may 
occur as an alternative response to the visual stimu- 
lation. We can not apply here simply the term reflex, 
but must say that the baby possesses an instinct, 
since the simultaneous stretching of the arms forward 
and the legs backward, and alternately the simul- 
taneous drawing in of all four extremities, are the result 
of selective grouping of nervous paths. That the 
alternation of stretching, drawing in, stretching, and so on, 
continues for some time can be explained by assuming 
that the sensory points of the muscles, tendons, and joints 
stimulated in either one position are by inheritance very 
closely connected with the motor points whose activity 
brings about the other position. The result of the simul- 
taneous drawing in and simultaneous stretching of the 
arms and legs is not necessarily, but may be, locomotion, 
provided either the front or rear extremities find a better 
hold on the ground, At first, it happens not infrequently 



CREEPING 145 

that this is the case with the hands rather than the feet, and 
the somewhat ridiculous observation is then to be made of 
a baby pushing himself away from the object exciting the 
eye. Once now, when the arms and legs are being drawn 
in, it happens that in consequence of an unusually strong 
nervous process one of the legs, drawn in with unusual 
force, gets under the body. When now, instinctively, the 
arms and legs are stretched, this leg, resting with the 
knee on the ground and bearing the weight of the body, can 
not slide over the ground, but pushes the body forward. 
The eyes are thus brought nearer the exciting object and, 
therefore, receive the same stimulation as before, only 
still stronger. The nervous process resulting from this 
stimulation now tends to take the path into the leg drawn 
under the body rather than into the other, because it is 
attracted in this direction. It is deflected by the flux 
resulting from the excitations of the sensory points of 
the knee and the muscles and tendons of the leg drawn 
under the body, whose corresponding motor points are, 
of course, in the muscles of the same leg. Thus the 
alternate stretching and drawing in occurs chiefly in this 
leg. The baby learns to creep on one leg. 

Why does not the baby, one may ask, learn just as 
readily to creep, at once, on both legs? The answer to 
this question is not that this is impossible, — only that it is 
less likely. During the first year the legs move, in the hip 
joint, much more readily sideways, than in later life. This 
i> due to the position of the fetus before birth, which chan- 
but gradually after birth and enables infants even for 
years to put their toes into the mouth, a feat impossible 
in later life, as we all know. When the baby is lying on 
the stomach and the legs are drawn in, the legs are not 
likely to gel under the body, but move outwards, in frog 
fashion. At the ninth or tenth month, however, the child 



146 HUMAN BEHAVIOR 

begins to roll over, and when now, in consequence of an 
unusually strong stimulation, the drawing in of the legs 
is accompanied by a rolling movement of the body toward 
one side, a chance is given for one of the legs to get under 
the body. It is most natural, therefore, that the creeping 
on one leg should be learned first. After some skill has 
been attained in this, the other leg is likely to get under 
the body too, and the baby then creeps on both legs. 
We stated that creeping usually makes its appearance 
about the time when the baby has learned to pull himself 
up and to walk along pieces of furniture. Creeping now 
has a pronounced influence on the child's progress in 
upright locomotion, in either of two ways. (1) As soon as 
the child has learned to creep on both legs — or knees, if 
we prefer this word, — he easily gets from the lying 
to the upright position without depending any longer on 
pieces of furniture or other objects which he can grasp, 
for the change from creeping to squatting is easy. With- 
out being able to stand up from the ground freely, walking 
is of but limited usefulness. Thus creeping contributes, 
though indirectly, toward perfection in upright locomotion. 
(2) If, however, free walking is not yet a firmly established 
habit,, the newly acquired form of locomotion, creeping, 
may so seriously interfere with the acquisition of that other 
habit as to hold it back for several months. Children 
who early become skilled creepers, usually learn to 
walk freely two or three months later than those children 
who little or never creep. This is comprehensible enough. 
The creeping child is not so exposed as the walking child 
to falling and to the consequent pain stimulation with its 
varied and strong motor responses, interfering by deflec- 
tion with the learning process. Further, creeping brings 
the young child more quickly to the object which stimu- 
lates the child's eyes than unskilled walking, and thus as- 



CREEPING AND WALKING 147 

sures the repetition of the creeping movement by the rep- 
etition of the stimulus from nearer by, much more than 
walking assures the repetition of the walking movement. 
In other words, the very nature of the case makes 
rapid improvement of skill in creeping more likely than 
of skill in walking; and when one form of locomotion has 
once been well learned, the other kind of locomotion, 
not yet well learned, is excluded by the simple rule of the 
effect of different resistances of various nervous paths, 
until, at a later time, new conditions arise. Some have 
drawn the practical conclusion, that therefore parents 
must prevent their children from creeping whenever they 
are seen to try it, before having become skilled walkers. It 
seems so simple : if creeping delays walking, stop the creep- 
ing and hasten thereby the walking. This conclusion, 
however, implies several important assumptions. First, 
walking is assumed to be the only kind of locomotion 
needed by a human being. This is somewhat doubtful. 
Not that we wish to assert that grown people ought to 
make frequent use of creeping movements, but it is highly 
probable that a complete analysis of our motor activities 
in later life would show of the elementary activities 
which are exercised in creeping many applications in 
new combinations. If this is true, the suppression of this 
exercise during infancy would be a grave mistake. 
Secondly, one must not think that the suppression of 
creeping before walking must be harmless since, after 
walking is thoroughly established, the child may be per- 
mitted to creep and thus exercise the same activities. 
Who knows whether exercise, then, brings about the 
same results in the education of the nervous system 
which it might have brought about previously? As long 
Bfl we know nothing about this question, it is hazardous 
to try to improve upon nature because we, as parents, 



148 HUMAN BEHAVIOR 

happen to bo exaggeratedly proud of our children's early 
accomplishments in walking and indifferent to all other 
kinds of motor accomplishments. Different children differ 
greatly in different talents, and we know that their suc- 
cess in life depends largely on the proper training of the 
most pronounced talent of the individual. It is 
possible, even highly probable, that a special talent 
means merely a special form of interconnection of 
the fundamental reflexes common to all; and such 
special interconnection may early show itself in 
such phenomena as this, where creeping does or does 
not precede walking. We might then really inter- 
fere with the child's most favorable development if 
we try to arrange the fundamental reflexes in groups 
different from those intended by nature. 

To these arguments, of course, some one might rejoin 
that he does not feel convinced that to prevent a child 
from creeping during a few months can be of such con- 
sequence, positively or negatively, to his later intellect- 
ual and moral development. Very well then, we can 
answer that to make a child walk freely at the age of 
twelve months, instead of letting him use for locomotion 
creeping during the thirteenth and fourteenth and free 
walking only from the fifteenth month, does not seem to 
bo of much significance for his later life either. The safest 
course in education — in this simple case as in the most 
complex problems of educational theory — is probably the 
one which interferes least with the development designed 
by nature and which trusts nature rather than tradi- 
tional ideals of education or, worse, parental vanity, un- 
less we have the most certain — experimental — evidence 
that in this or that way nature can be improved upon. 

Before leaving the discussion of creeping, let us mention 
two further accomplishments connected with its develop- 



FREE SITTING UP 149 

ment. The creeping child has acquired a second position 
of rest in addition to that of lying : he can rest at any time 
in a sitting position. It is true that children can sit, with 
support in the back and at the sides, when a few weeks 
old, and that they can sit on the floor without any further 
support when about six months old. But the ability to 
sit does not include the ability to seat himself, to sit 
up. The latter comes with creeping. The creep- 
ing child can sit up on the plain floor on which no objects 
offer themselves to his hands to be taken hold of. 
Thus when tired, he can take for resting the sitting as well 
as the lying position, and he often takes the former 
owing to the multitude of sensory-motor reactions of 
the nervous system which are only in this position possible. 
For example, the child when sitting can freely turn his 
head. 

The creeping child further acquires a play of his hands 
formerly impossible. During the first half year, whenever 
the child takes anything in his hands, he almost invariably 
puts it into his mouth, and often, when he has nothing 
in his hands, he puts one or more fingers in his mouth. 
These reactions become less frequent when the child begins 
to creep and sit up. Objects can now call forth numer- 
ous other responses. The child learns to push or throw 
away things, to creep after them and take them again; 
and this more complicated game, more likely to bring about 
repetition of activity by the repetition of stimulation 
of the eye and, consequently, more likely to become a 
strong habit, gradually supersedes the simple reflex of put- 
ting things into the mouth. It is the exceptional child 
that retains the finger sucking habit after the acquisition 
of locomotion. 

We stated above that children learn to stand freely, 
that is, to balance the body continuously in the upright 



150 HUMAN BEHAVIOR 

position, before they learn to move in this position. While 
this is generally true, there are also exceptional cases 
where children, being held in the upright position, are 
suddenly attracted by an object, perhaps the mother's 
voice, and start off running successfully five or six steps 
until they have reached the object. In such a case 
a child really learns to walk before he has learned to stand 
without support. However, as a rule, a child learns first 
to stand; and then, standing, in response to a stimulation 
of his eyes by an object, he moves one leg slightly toward 
the object, shifts his weight so that it rests on this leg and 
draws the other leg after, secures his balance, then moves 
again the first leg toward the object, and so on. One 
might call this form of locomotion walking on one leg only. 
In a week or two this one-sidedness gices place to the regu- 
lar form of walking in which both legs take part equally . 
For many months thereafter, however, a child's walk 
remains clumsy because the legs are kept so far apart, 
owing to the anatomical fact already mentioned that 
this opening of the legs sideways is the normal position 
until birth, which but gradually changes into that of the 
older child and adult, and also to the fact that balanc- 
ing is easier in this position. 

If walking is thus the outgrowth of standing, it is well 
to "encourage" free standing as much as possible after 
the baby has learned to stand while holding to things. 
What does it mean to "encourage" him? Let us reduce 
the process to its essential elements. (1) The child, when 
beginning to tumble, reflexly draws in his legs. (2) He 
lias often tumbled, when standing and losing the hold of 
his hands. (3) Subsequently, by a "variation of response" 
he draws in his legs at once (in other words, he sits down) 
when standing and losing the hold of his hands. But hecan- 
not practice balancing his body if he sits down. Therefore 



ENCOURAGEMENT 1,51 

(4) we give his hands the same or similar sensory impres- 
sions as if they were supporting the body. For example, 
we let the standing child grasp for support a small stick or 
pencil which we are holding, and then, gradually, we cease 
to hold it. The child then balances and, although nothing 
supports him, receives almost the same stimuli in his hands 
and eyes as if he were still supported by the stick in his 
hands. The process of balancing suffers no sudden inter- 
ference by a new stimulation (caused by the withdrawal 
of an object from his hands) and its reaction of sitting 
down. The "encouragement" which we give the child 
is therefore a purely negative event in the education of 
his nervous system : we keep an obstacle out of the way. 
After the establishment of free locomotion, further 
activities make their appearance, which are often referred 
to as the constructive and destructive instincts. It 
seems very doubtful, however, whether it is justifiable 
to speak of such instincts. A child, let us say, picks up 
one of a number of wooden blocks lying about in his room. 
He receives the visual stimulation of a similar block, and 
since the nervous path is still favored by the reduction of 
the resistance due to the previous stimulation, reacts in 
the same way, walks towards it and puts on it his hand 
in which he still has the first block. Since now, he cannot 
pick up the second block, he opens and raises his hand and, 
there, has before him a structure, one block upon another. 
Since this double block is a more striking stimulus than any 
of the single ones, it is quite natural that he returns to it, 
after having picked up one more of the blocks lying about. 
I> not all the so-called constructive activity simply a more 
or less complicated habit of the same kind as this very 
simple example? This habit of gathering and piling up 
must develop from the reflexes and habits which we have 
studied thus far, provided the child is surrounded by things 



152 HUMAN BEHAVIOR 

which are sufficiently similar so that two or more of them 
together make a similar, but more intensive sensory 
impression than a single one; and what child does not live 
under such surroundings? It is hardly necessary, then, 
to assume a mysterious particular instinct of constructive- 
ness. That the habit of taking to pieces, which is to be 
derived from the ordinary reflex of grasping, becomes 
united with this habit of putting together is plain enough, 
for taking apart brings about ever new opportunities for 
putting together. Thus develop constructiveness and 
destructiveness as co-operating habits. 



TWELFTH LECTURE 

Repetition of motor activity characteristic of learning 
in childhood. Variation of the order of earliest accomplish- 
ments. Speech organs: whispering and singing. First 
speech sounds. General and specific resistances of neurons. 
The motor outlet of a group of successive nervous processes 
determined by the temporal order of the qualitatively different 
processes. The general resistance as well as the specific 
resistance reduced by any special flux; but the reduction of 
the specific resistance outlasting that of the general resistance. 
Possibility of a particular distribution of specific resistances 
resulting from experience. 

OF the motor activities of early childhood we 
have briefly discussed thus far the adaptive 
movements of the sense organs of the head 
and the fundamental activities of the hands 
and feet. All the processes of learning which we mentioned 
can easily be placed in the classes distinguished by our 
theory of nervous activity. Most of them are simply 
variations of response, some are kinds of condensations. 
That the learning process is so quick in all these cases is 
largely due to the fact that the reflexes in question quite 
naturally lead either to an exact repetition of the stimulus 
or to a stimulus similar to the first and even more powerful 
— as when a baby piles up blocks. Even when a new 
stimulus caused by the first reaction is dissimilar to the 

153 



1 5 1 HUMAN BEHAVIOR 

first, it may take the path to the same motor point, either 
according to the law of deflection, or because of the 
temporarily lessened resistance in that direction, or 
owing to both these causes. It has become customary to 
refer to these repetitions of motor activity by the term 
"circular reaction." Such a special term is useful as it 
emphasizes the typical character of learning in early 
childhood in comparison with learning in later life, when 
the conditions are more complex and repetition of the 
motor activity rarely results. But let us not forget that 
the term "circular reaction " is not itself an explanation and 
would be an additional mystery unless we explain the 
facts themselves as we have very briefly attempted to do. 

Let us emphasize that, whenever we spoke of a particular 
kind of movement as preceding in human growth another 
kind, we wished to indicate merely the most common 
serial order of development, and that individual deviations 
from this order, displacing relatively for four or five 
months this or that element of action, are common too. 
Parents should neither be alarmed nor think that they 
have special reasons for paternal pride if they observe 
that their children do this or that several months later 
or earlier than other people's children, or that similar 
differences appear among their own children. Human 
life during the first — and even second — year is so elemen- 
tary, that any conclusions with respect to the enormously 
complex life of the future have as much value as the 
oracles of antiquity. 

The new-born baby is so helpless a creature that, if 
experience did not teach the contrary, one could hardly 
believe that such a being could survive the accidents with 
which he must be daily confronted. When he has reached 
the age of fifteen months, it seems much less improbable 
that he will succeed in the struggle with the world. He 



SPEECH 155 

has learned to use his sense organs, he has acquired the 
ability of locomotion which he daily improves by adding 
further skill in walking, running, and climbing, and he 
has learned to use his hands so that only further exercise 
is wanted to enable him to shape the world in accordance 
with his needs. Yet, at this age it is still easy to recognize 
that all the diversified human power is merely a complex 
of a small number of natural laws because we can still 
trace the child's power back to its sources. Of course, 
the few muscular activities which we have mentioned as 
characteristic of the behavior of the infant, are not really 
so simple as we have — intentionally — represented them, 
but are movements executed each by a large group of 
muscles and permit each many modifications, according 
as the one or the other muscle in the group receives the 
stronger nervous impulse. During the second year the 
complications grow almost into the infinite, especially 
during the second half of this year, when the child learns 
to use more and more effectively its speech organs. Never- 
theless, we shall convince ourseves that even now nothing 
happens but what can be derived from the laws of nervous 
activity previously stated and a few additional laws 
which we shall state below. 

It may be well here to make a brief statement as to what 
the essential factors of speech production are. There 
are two main classes of sound producing organs. The 
first class contains only the pair of vocal chords in the 
throat, at the end of the wind pipe. The vocal chords are 
comparable to an ordinary musical wind instrument. 
They produce, when the mouth organs leave the out- 
streaming air unobstructed, pure musical tones. With- 
out the vocal chords one cannot sing. With the vocal 
chords in a normal condition, one could sing even though 
the mouth organs were completely lacking. The vocal 



158 HUMAN BEHAVIOR 

chords might therefore be called the singing organ. On 
the other hand, the totality of the mouth organs, including 
even the nasal cavities, might be called the whispering 
organ. We can make ourselves understood even though 
we may be unable to sing; for example, when we are 
hoarse, we can still whisper. Our ordinary speech is a 
compound of whispering and singing, only that the latter, 
the "song" of speech, is not, in a musical sense, melodious. 

The first cry of the baby, immediately after birth, is a 
song, in the sense n which we have just used this word. 
It is only two or three months later that the growth of the 
nervous system has progressed far enough to make possible 
the reflex production of speech sounds. Naturally, first 
those speech sounds are called forth, which require the 
smallest amount of sensori-motor activity, df muscular 
contraction. These are the guttural sounds, produced 
by the mouth organs located farthest back, near the 
throat, and the dent;a'l sounds, in the production of which 
the teeth (or gums) co-operate with the tongue. Neither 
guttural nor dental sounds require the lips. It is natural 
again, that of the various guttural and dental sounds 
those are produced first which require the smallest amount 
of muscular work. We are therefore most likely to hear 
first such sounds as ga or goo and da or doo, later the sounds 
of k, /, etc. The accompanying vowel depends, in accord- 
ance with the laws of acoustics, on the measurements of 
the cavity which the mouth happens to form at the 
moment. Labial sounds occur several months later, 
since the tension of the lips requires more muscular work: 
we then begin to hear b and m and nasal n. The popular 
notion that the first words pronounced by a baby are 
papa and mama, is an illusion. 

One of our tasks in connection with speech is to explain 
how stimulation of the ear by different words, for example, 



TEMPORAL ORDER OF STIMULATION 157 

by the syllables ga and da 9 can call forth definite and 
different motor responses not on'y of the speech organs, 
but of any motor organs of the body. Here we are con- 
fronted by a difficulty which hitherto, in order to avoid 
complication of the discussion, we have intentionally 
evaded, but which we must now face. The question, 
Why does excitation occur at a definite motor point? 
we have always answered thus: Because over the path 
from the definite sensory point excited to this motor 
point the nervous flux finds less resistance than on any 
other path. Now, it is plain that stimulation of the ear 
by the syllables ga or da can not mean the stimulation of 
two different sensory points. It is true that the theories 
concerning the physiological processes in the ear show 
wide differences of opinion; but that the difference of da 
and ga is simply a local difference of sensory points from 
which the two nervous processes start, no physiological 
theory is likely to assert. That a nervous flux takes the 
path toward one motor point rather than toward another, 
must depend, not exclusively on the sensory point whence 
it comes, but sometimes also on qualitative differences of 
the flux itself. The importance of the role played by 
qualitative differences of nervous processes becomes still 
more apparent when we consider the fact that words 
differ, not only in the quality of the various stimuli, but 
especially in the temporal order in which the sounds follow 
each other. For example, the main difference between 
the words cat and tack consists in the difference of the 
temporal order of a small number of sound qualities. 
There is no doubt that such non-spatial differences of 
stimulation are sufficient to bring about spatial differences 
in the motor response. 

In order to explain these facts, it is not enough to speak 
of the resistance of a neuron. We must speak of a general 



158 HUMAN BEHAVIOR 

resistance and specific resistances to particular kinds of 
flux. How is it possible for a single conductor to have 
several specific resistances? We can understand this if 
we assume, as we have previously done, that a nervous 
flux is a wandering of ions. In a highly complex chemical 
substance like that which makes up nervous tissue, many 
kinds (hundreds or even thousands) of molecules may 
serve as ions. Our purely mechanical analogies, of course, 
become insufficient at this point, for, as soon as we assume 
different kinds of ions, we would have to use as analogy 
a stream of which not always the whole substance, but 
sometimes only these, sometimes only those of the parti- 
cles composing the substance may be in motion, while 
other particles uniformly distributed through the whole 
substance may remain at rest. This is something like 
the streaming in filtering and in osmosis, but even more 
complicated than such processes. 

The assumption of specific resistances of any neuron is a 
brief expression of the fact that the motor outlet of a nervous 
process may be determined by the quality of the flux. Now 
we must find a way of expressing by a picture the fact 
that the motor outlet of a definite group of processes 
quickly succeeding each other may be determined by the 
particular temporal order of the qualitatively different 
processes, in order to make plain that, for example, the 
response to the word cat may and does differ from the 
response to the word tack. Let us use for this purpose 
the diagram of figure 42. In this figure S° represents a 
peripheral sensory point; S 1 a central sensory point from 
which several neurons pass on in different central direc- 
tions; Mabc an d M 2 de f central motor points from each 
of which numerous neurons pass on in different peripheral 
directions. Imagine that the words cat and tack consist 
of two sounds, let us say, ca and ta, and that the difference 



GENERAL AND SPECIFIC RESISTANCE 159 



of the two words lies in the order of succession of these 
two sounds. While this is only very approximately true, 
the simplification thus brought about is justified by 
our purpose. Suppose that the nervous process belonging 
to the sound ca is x, that the nervous process belonging 
to the sound ta is y, and that in Figure 42 the neurons 
S 1 Sl bc9 Sl bc M 2 abc , M 2 def M}, and M)M f have an extra- 
ordinarily low specific resistance for the flux x (as indicated 



^abc Sde^ 




® 



n. 






n, 



© 



■■c S° ^d ^e Mf 

Fig. 42 — Motor response dependent on temporal order of stimulation. 



in the figure by the letter x inclosed in a circle) and the 
neurons S^/, S 2 def M 2 def , M 2 abc Ml and M\M C an 
extraordinarily low resistance for the flux y (as indicated 
by the letter y inclosed in a circle). Our task is to explain 
why the motor response occurs at M c when from *S° the 
flux x precedes the flux y, and at the different point M f 
when the temporal order of x and y is reversed, — to show 
that this difference of response is possible. We shall show 
it in exact mathematical terms. 



160 HUMAN BEHAVIOR 

Suppose the fluid quantity passing through one neuron 
in a unit of time to be equal to G in case general resistance 
is effective, equal to S in case specific resistance is effective; 
and that in the latter case the flux is greater, so that S 
is larger than G, perhaps a multiple of G. Suppose further 
that the resistance between two "levels" of the nervous 
system distant the length of one neuron is equal to the 
reciprocal value of the fluid quantity passing in a unit of 
time. Then, for the flux x, the resistance between S 1 
and Mibc ls | since the fluid quantity for each of the two 
neurons S S^ c and S abc M abc is S and the resistance of 
each neuron accordingly §. The fluid quantity passing 
parallel through the neurons which lead from M 2 ahc to the 
periphery is, for the flux x, G multiplied by the number 
of branches from M 2 ahc , which we shall call N. The 
resistance between M 2 ahc and the periphery is then ^ 
multiplied by 2, since each branch has the length of two 
neurons. The total resistance, for the flux x, between S 1 
and the motor periphery represented by the total group 
of motor points M a9 M b , etc. (let us call it L, being on the 
left side of the diagram) is therefore 

T _2 , 2 _2(N G+S) 
-^ S^NG NGS 

For comparison, we must now determine the resistance, 
for the flux x, between S l and the motor periphery repre- 
sented by the total group of motor points M d , M e , etc. 
(let us call it R, being on the right side of the diagram). 
The resistance between S 1 and M de f is ^. The resistance 
between M 2 ef and the motor periphery is to be found as 
follows. The fluid quantity passing parallel through 
the neurons which lead from M 2 ef to the level one neuron 
nearer the periphery, is S plus (N— 1)G, since one of the 
neurons branching off from M 2 ef has for x a specific resist- 
ance, g, and the (N— 1) other neurons have the general 



GENERAL AND SPECIFIC RESISTANCE 1G1 

resistance ^. The resistance between M 2 def and the 
periphery is then the reciprocal value S _|_( N _ 1)G , to be 
multiplied by 2 since each branch has the length of two 
neurons from M 2 e f to the periphery. Consequently: 

p_2 i 2 = 2(S +NG-G + G _ 2 (S + NG) 

11 G r S + (N-l)G G(S+NG-G) G(S+NG-G) 

In order to compare the magnitude of L with that of R, 
let us form the ratio: 

L_ 2(NG+S)XG(S+NG-G) _ S+NG -G 
R NGSX2(S+NG) NS 

Let us consider this formula in a few special cases. It 
appears that, when there is only a single motor branch 
at M 2 ahc as well as at M 2 def , that is, when N equals 1, L 
attains its maximum value, is equal to R, for 

L_ S+G-G _ n 
R S L 

With increasing N, the ratio ^ grows smaller, for each 
unit added to N is multiplied in the numerator only by G, 
but in the denominator by the larger value S. If N 
becomes a very large number, the ratio 

L_ S+NG-G 
R NS 

approaches more and more s , which is the lower limit of 
this resistance ratio, for in the numerator the constant 
value (S-G) becomes then infinitesimal relative to NG, 
so that the ratio reduces to 

limit k=gi=f<l 

We see, thus, that the advantage of the left side of the 
conductive system of Figure 42, which is equivalent to 
smallness of the resistance ratio ^, for the flux x, depends 
on two conditions, (1) on the degree by which the specific 
resistance \ is reduced below the general resistance q, or, 
in other words, by which the flux intensity S surpasses 



162 HUMAN BEHAVIOR 

the flux intensity G, (2) on the number N of the specific 
motor points belonging to the system. Now immediately 
after the termination of the flux x, the flux y takes its 
origin from the same point S°. In order to give x, n this 
theoretical discussion, no unfair advantage over y, we 
have supposed our conductive system of Figure 42 to 
offer to y all those resistances in the direction of "left- 
right" which it offers to x in the direction of "right-left." 
Accordingly, as the flux x found the lesser resistance from 
S° toward the left, so y would find the lesser resistance 
from S° toward the right, if nothing had preceded. Actual- 
ly the flux x has preceded the flux y immediately, and this 
fact, obviously, must be the cause which prevents the 
flux y from taking mainly the path toward the right of 
the diagram. To this causal relation we have to give 
expression in an assumption in the form of a general 
statement. We assume that any special kind of flux, 
say x, reduces not only the specific resistance, for x, of 
the neurons in which it occurs, but also the general resist- 
ance of these neurons; but we assume, in addition, that 
the reduction of the general resistance disappears under 
lack of function much more quickly than the reduction of 
the specific resistance. 

Let us see what necessitates the latter half of this 
hypothesis: clearly, the admittance that any specific 
resistance of any neuron can be the result of function as 
well as of mere inheritance. If the reduction by function 
of the general resistance did not disappear more rapidly 
than the reduction of the specific resistance, no neuron 
could 1)0 said to have any specific resistance distinct 
from its general resistance, save directly by inheritance. 
On the other hand, our assumption implies that during a 
short time directly after the termination of a particular 
flux, the general resistance may be regarded as being as 



GENERAL AND SPECIFIC RESISTANCE 163 

much reduced as the specific resistance. It is plain that 
this is of the utmost importance for any immediate suc- 
cession of two or more qualitatively different nerve 
processes. 

Let us make the application. The flux x from the 
point S°, taking its path largely over the left side of the 
system of Figure 42, is immediately succeeded by the 
flux y, likewise from the point S°. If y had not been 
preceded by x, it would have found toward the right, 
over Sd e f 9 a resistance less, in proportion to the ratio 
^Yg^^, than toward the left, over S 2 abc . But the general 
resistance of the left side having ust been reduced, in 
consequence of the flux x, there may be for y no more 
resistance to the left than to the right. Suppose, then, 
for simplicity 's sake, that the flux y divides equally at the 
point S 1 , where the first branching occurs. The part 
passing to the right divides again at M 2 ef . It divides 
about equally into N parts, since none of the neurons 
leading from M 2 ef to the N motor points has a specific 
resistance for the flux y. The part passing from S 1 to the 
left, divides at M 2 abc also into N parts, — but into unequal 
parts, since the neurons M 2 ahc M\ and M l c M c have a 
specific resistance for the flux y, all the others only the 
general resistance. If N is a rather high number, that 
is, if the peripheral branches are very numerous, the 
ratio of the flux reaching M c to the flux reaching any 
other single motor point on either side of the dia- 
gram, must be approximately as S to G. (The ratio ^ 
is the limit.) 

Summarizing now the total motor influence of x and y 

ether, we reach the following conclusion. Of x bul 

little flows into the motor points to the right. The main 

flow reaches the motor points on the left side, including 

M Ci but distributes itself equally over all these. Of y 



164 HUMAN BEHAVIOR 

a much larger (proportional to ^) part flows into M c 
than into any other motor point of the system. There- 
fore, the main motor response to the total stimulation x 
and y in this immediate succession occurs at M c . If the 
succession had been y and x, the main motor response, 
owing to the symmetrical relations of all the conditions 
concerned, would have occurred at Mf. We have thus 
demonstrated that the mere temporal relation of two stim- 
uli (x and y) may result in a spatial determination (at M c ) 
of the motor response. 

We wanted to explain the fact that a human being 
reacts to the word cat in one way, to the word tack in 
another way. In the diagram of Figure 42, which we 
have used for the explanation, we have supposed certain 
conductors to possess a specific resistance for one kind 
of flux, others a specific resistance for another kind. But 
that nature should by inheritance completely provide for 
such details of stimulation by such details of resistance 
distribution as those of this figure, is highly improbable. 
Our explanation is satisfactory only if we can show that a 
resistance distribution like that of Figure 42 may result 
from "experience" during the individual's life. 

In the middle of Figure 43 we find a reflex arch whose 
central points are named S\ and M \. This is one repre- 
sentative of the whole class of reflex arches connecting 
the sensory points in the muscles and tendons of the 
speech organs with the motor points in the muscles of 
these same organs. These reflexes are undoubtedly of 
more importance for the talking instinct of the young of 
the human species than any other class of reflexes affecting 
the speech organs. In our figure the sensory point of 
the reflex arch has been marked by the word k : nesthetic. 
This name is, of course, really too broad in its meaning, 
since it includes all sensory points found within any of the 



GENERAL AND SPECIFIC RESISTANCE 165 




166 HUMAN BEHAVIOR 

motor organs. More correct, but rather long, would be 
the name "kinesthetic of the speech organs. " The motor 
point of the same reflex arch has been marked by the word 
speech. Below it we find in the figure the syllable ca, 
which is to indicate that the kinesthetic sensory stimulation 
and the motor activity are both those of the speech 
organs pronouncing the syllable ca. One of the results 
of this motor activity is the production of the sound ca, 
the stimulation of the ear by this sound. The nervous 
process thus starting from the ear is deflected by the 
kinesthetic nervous process and takes its path from S d 
over S 2 cd , M 2 cd , and M \ into the speech organs. Thus 
the child may be supposed to learn to pronounce the word 
ca in response to the sound, to "imitate" the word habit- 
ually. But he learns to imitate also other words, for 
example ta. In this case the nervous process takes its 
path from the point S\ in a different direction, say, over 
S de9 M 2 de , and M\ into the motor point marked in the 
figure by "speech" and "ta." 

It is plain that the child, living in a human environment, 
is stimulated by the sound ca most frequently when such 
things as a "cat" or a "cap" or others whose names 
begin with the same sound, are present and stimulate the 
eye with unusual force, more strongly than the other 
things which happen to be there too. Consequently, 
the strong nervous process coming from the eye deflects 
the weaker one coming from the ear, makes it take its 
path from S 2 cd up to Sl bcd over M\ hcd down to M 2 ab , and 
thence to the motor periphery. Thus a specific resistance 
must be established for the flux corresponding to the sound 
ca, in the neurons leading from S\ to M 2 ab \ but practically 
no specific resistance for any flux corresponding to any 
of the sounds following ca in ca£, cap, etc., since the 
sound ca, common to all these words, occurs with so much 



GENERAL AND SPECIFIC RESISTANCE 167 

greater frequency. Thus the point S], becomes, so to 
speak, a branching point of specific resistances, for ca to 
the left in the figure, for ta by a similar process to the 
right, and for many other sounds in other directions which 
are not explicitly drawn in Figure 43. This is exactly 
what we pre-supposed for the point S 1 in Figure 42, with- 
out showing, at the time, how it could originate. The 
promise in this respect we have now made good. We 
still have to show, however, how in Figure 42 from the 
point Mabc to a special motor point (M c ) a second kind of 
specific resistance can establish itself. Figure 43 answers 
our question. Whenever a cat is before the eye, the 
nervous process from the ear is drawn towards M a (in 
Figure 43); and this nervous process contains regularly 
the specific flux corresponding to the t-sound. According- 
ly, the nervous path M 2 ah M l a M a must have a very low 
specific resistance for this flux, compared with any other 
path branching off from M 2 ab . This explains the second 
presupposition embodied in Figure 42, for we had supposed, 
there, that one of the N branches from M 2 abc to the 
periphery possessed a very low specific resistance for a 
second kind of flux. We were, therefore, entitled to the 
suppositions in Figure 42, and can rightly assert that we 
have demonstrated that the temporal order of qualitatively 
different stimuli may determine the motor point which 
responds. 



THIRTEENTH LECTURE 

A simple sensory excitation bringing about a temporally 
complex response. Some, but by no means all, temporally 
complex responses to a simple sensory excitation explainable 
on the basis of geometric-mechanical rivalry of motor organs. 
Multiform variation of response. Importance of kinesthetic 
sensory activity. Two stages in the development of speech. 
Reflex pointing and utterance of a dental sound. Left- 
handedness during the first months of life. Right-handed 
reflex pointing. Right-handedness and speech. Accented 
and gesticulating languages. 

WE have discussed the fact of a temporally 
complex stimulation, a word, producing 
one response at a definite motor point. 
But the reverse is of no less importance, 
— the fact of an absolutely simple sensory excitation 
bringing about a temporally complex response, for ex- 
ample, since we are just discussing speech, bringing about 
the pronunciation of a word, or of a whole sentence. We 
must not imagine, however, that the pronunciation of 
every — even the simplest monosyllabic — word presents a 
problem of this sort. When a child one year old 
begins to pronounce such syllables as ga or da, 
nothing is required to bring about the proper motor 
activity but an equal, or about equal, division of the 
simple nervous process into several branches simultan- 
eously. This is theoretically nothing new, a pure case of 

168 



TEMPORALLY COMPLEX RESPONSE 169 

sensory condensation. The muscles active in such a case 
in producing the second sound, the vowel, may be inner- 
vated at the same time with those active in producing 
the first, the consonant. Everyone can easily make the 
experiment which proves this. Get ready with your 
mouth organs to say ga, but stop short before the expira- 
tory "explosion." Then do the same for the syllable 
goo. You notice a great difference of position of the 
mouth organs and of tension of the various muscles, 
although the consonant beginning the word is identical 
in both cases. The mouth organs, it appears, are ready 
at once to produce both sounds, consonant and vowel; 
and it may be altogether a matter of geometric-mechanical 
conditions — an organ being incapable of moving at once 
in two opposite directions — that actually the consonant, 
since it cannot occur simultaneously, precedes or follows 
the vowel. Try the case of the vowel preceding the 
consonant. Get ready to say og or ot. Again the mus- 
cles, especially those of the tongue, have entirely different 
tensions before even the vowel o is heard; that is, the 
muscular tensions needed for the second sound begin at 
the same time as those needed for the first. It is possible — 
indeed probable — that in the pronunciation of such words 
as god and dog there is no difference at all in the temporal 
order of the nervous activities involved, but a mere dis- 
tribution of the relative resistances of the nervous branches 
serving simultaneously as conductors, to the effect that, 
in the one case, the muscular "g-tension" is stronger than, 
and thus becomes outwardly effective before, the "d- 
tension," in the other case the reverse, — the o-tension 
being of intermediate intensity in either case. 

Let us admit that this is the true explanation of the 
pronunciation of many a word, but let us also be aware 
that this does not include the assertion that, whenever 



170 



HUMAN BEHAVIOR 



any word is pronounced, its pronunciation results just in 
this way. Nothing can be more misleading than the 
tendency to believe that a certain event, in the complexi- 
ties of human life, must regularly have the same cause. 
There is no question that the pronunciation of a long, 
polysyllabic word — not to mention a sentence — can not 
be the outcome of a purely geometric-mechanical rivalry 
of the several speech organs crowded together in and about 
the mouth and excited with different intensities. If a 
short word often does come about by this rivalry, it often 
may and does come about in the way typical for long 
words and sentences. What is this latter way? 

Let us imagine, in the following discussion, a child so 
far advanced in experience that he responds to any simple 
speech sound impressing his ear by producing a similar 
sound with his own speech organs. In Figure 44, S k 
denotes (k equals kinesthetic) a sensory point within the 







A 


Ik 






SbcdK 






nk 


/ \ 


/ 


,\ 


1 \ 


1 


/ 


— <" 

) 


3' 



Mb Mr M d M K Sk 

Fig. 44 — Multiform variation of response. 

muscular and tendinous organs of speech, or, rather, 
that whole group of sensory points which are stimulated 
by the tensions of the speech organs during the production 
of any definite sound, say, the word baby. The motor 
ending of the reflex arch S k M k is of no direct interest to 
us; we might imagine that M k represents the motor activ- 
ity of saying "baby," w T hich leads again to stimulation of 



TEMPORALLY COMPLEX RESPONSE 171 

S k , but we must note that in the following figure another 
point, M a will be supposed to take this function. We 
know that from S k over a higher center, S bcdk M bcdk , a 
route of low resistance may be established in the direction 
of numerous motor points, M b , M c , M d , etc., — each of 
which represents here rather a group of motor points 
active in the production of one definite speech sound than 
a single point. To take a concrete example, — a child 
happens to say "baby" and the mother's answering 
"cry," "hungry," "tired," etc., causes the child to pro- 
nounce one of these same words in succession to "baby." 
While the word baby is — probably repeatedly — produced, 
the kinesthetic nerve process starts from S k . At the 
same time the auditory process (not represented in the 
figure) resulting from the mother's answer leads to the 
imitative motor activity at either M b9 or M c , etc. Of 
these two processes, the former is attracted and deflected 
by the latter, and the child, instead of saying once more 
"baby," says now "cry," another time "hungry," etc., 
whatever the mother has said. The deflection of the 
nervous process originating at S&, from S\ upwards (in 
Figure 44), leads then to a multiform variation of response. 
The actual response at any future time, on the basis of 
this variation of the nervous path, to a stimulation of S k 
occurs either at M bi or at M c , or at M d , etc., according as 
adventitious circumstances happen to favor the one or the 
other of these points. That the variation must be multi- 
form, is plain enough, for many kinds of word successions 
having the same first word must needs occur in the experi- 
ence of a child surrounded by older people. What, then, 
may be such an adventitious circumstance as just men- 
tioned, making the selection among the motor outlets of 
the multiform nervous path? Here we approach the real 
problem set before us at the end of the previous paragraph. 



172 



HUMAN BEHAVIOR 



Figure 15 is an elaboration of the directly preceding 
figure. S° is a sensory point at which, we suppose, an 
absolutely simple nervous process originates, for example, 
the sound of a baby crying at a distance. At S a branch- 
ing of the nervous conductor brings about a division of 
the process to the left and right. We suppose that the 
resistance to the left is less, so that the main flux occurs 
in this direction, much less to the right, as indicated in 
the figure by the conductors to the left being drawn in 




Fig. 45 — A simple stimulus calling forth a temporally complex response. 



double lines. The motor response occurs practically only 
at M ai notwithstanding a certain amount of muscular 
tension elsewhere, especially at M h . Now, imagine both 
these points, M a and M b9 to represent two groups, partly 
overlapping, of muscular organs of speech. The sound 
actually pronounced is then the one corresponding to 
M a ; the other, corresponding to M b , is excluded by geo- 
metric-mechanical rivalry, the same organ being incap- 
able of moving in two opposite directions and follow- 
ing by necessity, the stronger pull, — a very ordinary 
evenl in animal life. The pronunciation, through 
its muscular tensions, stimulates a whole group of the 
kinesthetic sensory points in the organs of speech; and 



TEMPORALLY COMPLEX RESPONSE 173 

the group of sensory points thus affected is exactly, let 
us say, the one which we have formerly called S k . Then 
a second word must be pronounced in response to the 
stimulation of S k ; and of the many responses possible, 
at M b , or at M c , or at M d , etc., the one must actually 
occur which is favored by the adventitious circumstance 
that directly before this moment a nervous flux, although 
weak, has passed from S 1 over Sf and Ml through the 
neuron M I M b . That is, under the conditions embodied 
in Figure 45, a simple stimulation of S° must result in a 
temporally complex response, a succession of two muscular 
activities, first at M a and then at M b . 

Still the question is left if in our demonstration just 
completed we had a right to pre-suppose such a branching 
of the nervous conductors as represented by Figure 45 
at the point S 1 , which means that saying "cry" (M b ) 
is a rival, but weaker, response to a certain stimulation 
at S° (e. g., a sound coming from a distance) that is 
actually responded to by saying "baby" (M a ). We had 
a right to pre-suppose this for the following reason. The 
child in question is sufficiently advanced in experience to 
respond to a simple speech sound heard by pronouncing 
it imitatively, — this we have assumed. We only have to 
ask, therefore, whether he has the opportunity of hearing 
grown people say both "baby" and "cry" frequently 
while a crying baby impresses the sensory point S°. Of 
course, this must be the case, and surely, too, the word 
"baby" is under these conditions more frequently used 
than the word "cry," so that of the two paths establishing 
themselves from S l upward the one leading to M a must 
have its resistance reduced much more than the one leading 
to M b . 

We have shown, thus, how experience can train the 
nervous system in such a way that one simple stimulation 



174 HUMAN BEHAVIOR 

is responded to by a succession of motor activities, by a 
temporally complex action. We do not assert that every 
training of this kind must conform with figure 45. There 
may be hundreds or thousands of other possibilities of 
bringing about a similar result. To have demonstrated 
one such possibility, as an example, is sufficient for our 
present purpose. Let us use this opportunity, however, 
to point out a fact of much general importance for all 
training of temporally complex reactions, namely, the 
necessity of kinesthetic sensory activity. If it were not 
for temporally complex reactions, kinesthetic sensory 
points would be rather superfluous. Why should any 
animal respond by particular reactions to tension in its 
muscles and tendons? The biological purposes of activity 
are, mainly, protection and nutrition. Neither is, as a 
ride, served directly by an animal's reacting upon internal 
tension. But a definite temporal order in a very complex 
reaction could hardly be acquired, as Figure 45 shows, 
without the mediation of kinesthetic sensory points, 
enabling the first motor activity to determine — in co-opera- 
tion with further conditions — the second, the second to 
determine the third, and so on. The greater the com- 
plexity of an animal's anatomy, the greater is the need of 
temporal order in its compound motor activities. Thus, 
indirectly, the kinesthetic sensory points come to serve 
the purposes of nutrition and preservation, to be ultimately 
as indispensable as the sensory points on the surface of 
the body. But a direct reference to any purpose can 
hardly ever be found in the kinesthetic sensory activity, 
except where — as it happens especially in the highest 
animal, in man — the performance of a skillful motion 
becomes itself a purpose, severed from all "practical" 
significance, for example, in athletic sports. 

On the basis of our views concerning the nervous 
conditions of speech functions, we may adopt a distinction 



KINESTHETIC SENSORY FUNCTION 175 

which is often made by those interested in the growth of 
speech. We may distinguish two stages in the develop- 
ment of speech, the early prattle of a child, consisting 
mainly of monosyllabic words, and the more highly 
developed — often, but only with partial justice, called 
exclusively the "imitative" — formation of longer words 
and sentences. The early prattle of a child depends on a 
branching of the nervous process so that numerous motor 
points receive the excitation simultaneously or almost 
simultaneously. The branching of the nervous conductor 
is then similar to that in the special process of learning 
which we have called sensory condensation. But this 
branching may be completely inherited. The speech 
organs usually produce both a consonant and a vowel, 
but one precedes the other owing to geometric-mechanical 
rivalry. Even sounds consisting of two consonants and 
a vowel may be produced in this way, like gook. And 
polysyllabic words too: very easily reduplications like 
dadadada, or words like goocka, booppa, hoppa. Such 
words are characteristic of the second year of life. It is 
a mistake to think, however, that the term imitative is in 
no way applicable to this stage. In this — in the main 
monosyllabic — prattle, as in his later talking, the child is 
influenced by what he hears grown people pronounce. 
The second stage, from the end of the second year 
continuing really all through life, is governed by kines- 
thetic sensory functions, as illustrated in Figure 45; and if, 
as often in the nervous disease of aphasia, the kinesthetic 
functions are interfered with, the grown person retires to 
the prattling stage. Let no one think, however, that the 
simpler function, governed by geometric-mechanical 
rivalry of the speech organs, has ceased to exist in the 
second stage. Many kinds of lapses of speech in grown 
people and in children prove the contrary. When a child 



178 HUMAN BEHAVIOR 

says tome instead of come or dood instead of good, it is not 
necessarily, as one might be inclined to believe, because 
he can not pronounce gutturals, — they are the class of 
consonants most easily produced. Most probably, in such 
a case, the nervous function described in Figure 45 is not 
perfected, and simultaneous innervation, by means of a 
mere branching of the nervous conductor, governs the 
pronunciation. Then we understand why tome should be 
pronounced instead of come, for the branching of the 
nervous conductor is more ready to serve / and m together, 
both of which are produced by the speech organs located 
in the front of the mouth and co-operating naturally 
in many ways, than to serve k and m together, of which 
the former is produced by speech organs located in the 
back part of the mouth and therefore less naturally 
co-operating with the other. That any imaginary difficul- 
ty of producing guttural sounds need not have anything 
to do with the case, is demonstrated by the example of a 
German-speaking child who insisted upon saying kragen 
instead of tragen, — certainly not because gutturals are 
more easily pronounced than dentals, but because the 
other significant consonants of the word, the German r 
and the g, are both gutturals, with a common nervous 
conducting apparatus. 

In our ninth lecture we mentioned the reflex of pointing 
with the index finger at a thing which impresses the eye. 
We said that this reflex appears at about the same time 
when the first articulated sounds (usually guttural and 
dental- ga and da) are instinctively produced by the 
baby. But the act of pointing is not accompanied by a 
guttural, but by a dental sound — the baby pointing and 
saying dadada. We recall, too, the interesting fact that 
in all Germanic languages the demonstrative pronouns 
begin with a dental sound. Why does the baby say da 



REFLEX POINTING 177 

when pointing at anything, and not ga? The answer is 
to be found in the same considerations which we have 
just applied. The act of pointing sets in motion one of 
the extremities of the body. The nervous process, one 
of whose divisions goes into this extremity, can naturally 
reach by one of its other divisions more easily the muscles 
of the frontal part of the mouth, belonging to the periphery 
of the body, than the muscles of the throat, belonging to a 
different, an internal, system of muscular activity. Try 
yourself to accompany a pointing movement by a dental 
or a guttural sound. The latter seems less natural. 

When the reflex of pointing first occurs, we notice that 
the pointing is done far more frequently with the right 
than with the left hand, whereas previous to this time the 
right hand is by no means favored in action. The func- 
tional connections between the reflex of pointing, the 
growth of speech, and the development of right-handed- 
ness, are so interesting that we must discuss them more in 
detail. A baby two or three months old, in using the 
hand, for example in order to put the fingers into the 
mouth, unquestionably gives preference to the left 
hand in about two-thirds of all cases. That is, one 
observes during the first few months about two activities 
of the left to one of the right hand. Toward the middle 
of the first year this preference disappears, and both 
hands are now used with about equal frequency. This 
is also the time when speech sounds, although hardly 
yet imitative, become more frequent. During the second 
year — say, at the fifteenth month, making allowance for 
the enormous individual differences — the right hand 
begins to predominate, and about the same time speech 
enters upon that rapid development which insures to this 
art its being the distinguishing feature of a human being 
as compared with an animal. As little as it possesses 



ITS HUMAN BEHAVIOR 

speech in the human sense, can any animal be said to 
be right-handed or right-sided. In animals both sides of 
the body function about equally. 

It is probable, although not absolutely certain, that the 
totality of these facts may be explained in the following 
way. The left hemisphere of the normal human brain, 
as has been known for nearly a century, has functions 
different from those of the right hemisphere; not merely 
in so far as the right hemisphere is more closely connected 
with the left side of the body and the left more closely 
with the right side of the body, but through its significance 
for the functioning of the speech organs. Certain nervous 
paths, most probably those leading from the kinesthetic 
sensory points of the speech organs, have their higher 
centers in the temporal part of the left hemisphere exclu- 
sively, and when a person suffers from aphasia, it is in 
this part where a lesiofr is regularly found in a post- 
mortem examination. It is clear, then, that the growth 
of speech during the second year of life is coincident with 
and dependent on the inner development of this part of the 
brain; and since this part of the brain is also closely con- 
nected with the hands, but more closely with the right 
than with the left hand, it is to be expected that speech 
functions bring about activities of the right hand. Thus 
we understand why certain movements of the baby's 
speech organs are accompanied by pointing movements 
of the right hand, and why grown people, too, so fre- 
quently accompany their talk by gestures of the right 
hand. 

As to the time of the development of the right hemi- 
sphere of the brain in comparison with the left, we are 
entitled to a conclusion from analogy. The human 
brain with its complex functions is not ully developed 
until years after birth. The brain of larger animals of a 



LEFT-HANDEDNESS OF INFANCY 179 

longevity comparable to that of man, with its simpler, 
but no less important functions, is fully developed some 
months after birth. May not a similar rule govern the 
development of the left and the right hemispheres? The 
temporal part of the left hemisphere, with its highly 
complex speech functions, is not fully developed until 
years after birth- — so much we know. By analogy we con- 
clude that the symmetrically corresponding part of the 
right hemisphere, with its simpler, though no less import- 
ant functions, develops to maturity at a much earlier 
period. If this is so, activity of that hand which is 
governed by the right hemisphere, must become con- 
spicuous at a much earlier period than activity of the 
other hand. Indeed, the left hand, whose muse es are 
closely connected with the temporal part of the right 
hemisphere, is the preferred member in the activities of 
the first few months after birth. Thus the fact that a 
normal human child is at first left-handed and then 
changes into being right-handed, to remain so during his 
life, appears plain enough. 

Movements of the speech organs are likely to be accom- 
panied by pointing movements or other gestures of the 
right hand, or of both haftds because of the nervous 
co-ordination of the hands, so we said. Some languages, 
especially the English, habitually put an enormous vigor 
into the enunciation of one definite sound of each word 
or sentence. The English language, that is, is a strongly 
accented language. According to our law of nervous 
deflection we might expect that the strong nervous flux 
leading to the enunciation of the accented sound should 
interfere with the execution of the hand gesture. It 
seems that this explains the absence, or at least remark- 
able infrequency, of gesticulation in speakers using the 
English language. In the French language, on the other 



ISO HUMAN BEHAVIOR 

band, there is no accent worth mentioning, and the reflex 
gestures of the speaker are therefore fully preserved. 
Accent is thus a substitute for gesture. This explanation 

seems more generally applicable than the customary one 
referring to racial differences of temperament as the exclu- 
sive cause of the difference in question. Such a difference 
of "temperament" would remain both ethnologically and 

psychologically rather mysterious. 



FOURTEENTH LECTURE 

Spatial perception. Inherited responses to spatial form. 
Acquisition of unitary groups of conductors serving all 
objects of the same design. Mutual attraction of nervous 
processes of equal strength. Melody and harmony. Two 
kinds of tonal similarity. Neurons applying their specific 
resistances in various degrees to a variety of processes. 
Rhythm equals subjective grouping of objectively uniform 
excitations. Habits of performing group motions consisting 
of one chief and one or several preparatory movement* 
Xo counting in rhythmical perception. Why all common 
rhythms are of the doublet and triplet kind. 

THE function of the nervous system is said, by 
some, to have three aspects. But to distingiush 
them one must narrow his view to an exclusive 
consideration of the sensory function, the motor 
function, or the collecting and redistributing function of 
the system, of which none can have any separate exis- 
tance. How artificial the separation of these functions 
is, appears from our previous discussions. The function 
of the nervous system is always one which carries sensory 
excitations to motor points over short or long, relatively 
simple or 'complex paths. A distinction of different 
aspects of this single function merely offers convenient 
headings under which to place chapters of a prolonged 
discussion. Thus we may say that we are now to consider 
a certain sensory aspect of nervous function, namely that 

181 



183 HUMAN BEHAVIOR 

which is customarily referred to by psychologists under 
the name of the perception of space. The sensory points 
here in question are mainly those of the cutaneous surface 
of the body and the retinas of the eyes. The problem 
which concerns us is, broadly stated, this: How can we 
explain the fact that group stimulations of a particular 
geometrical design, occurring now here, now there on the 
sensitive surface, are capable, within limits, of calling forth 
identical motor responses although the sensory elements 
stimulated may be either entirely different or only 
partly identical? 




Fig. 46 — The simple perception of space. 

To state the problem less abstractedly, let us take an 
example. A triangle is before our eyes. We move, and 
the triangle appears on a different part of the field of 
vision, al H instead of at A, in Figure 46. The sensory 
elements stimulated in both cases are partly different, 
partly identical, as the figure shows immediately. We 
move again and the triangle appears again on a different 
part of the field of vision, at C. This time altogether 
different sensory elements are stimulated. In all three 
cases our reaction is about the same; if it is a speech 
reaction it consists probably in our pronouncing the word 
triangle. Whatever the reaction may be, on general 



SPATIAL PERCEPTION 



183 



principles of theoretical explanation we must be able to 
conceive of it, because of its definiteness and identity, 
as the result of a nervous flux proceeding somewhere 
within the nervous system from a definite single point. 
Our problem, then, consists in showing the possibility of 
all the nervous processes which come either from A 9 or 
from B 9 or from C 9 uniting in the same single point within 
the nervous system. From this point on toward the motor 
periphery the nervous process may then undergo all the 
influences hitherto described in general, leading to all 
kinds of variations and combinations of motor effects. 



Sx Sp S) 



Si 



Su 




[ { I I I 

Sa Sb Sc Sd Se 

Fig. 47 — Sensory points serving form stimulations. 

Figure 47 contains two classes of points which are 
marked with letters. The points marked S X9 S y9 S Z9 S U9 S p 
are those among which the central point just mentioned 
is to be found. They are quasi-sensory points, not located 
in the sensory periphery of the nervous system, yet to be 
regarded, in the light of all our previous discussions of 
function, as if they were truly sensory points. In them 
are collected the conductors which unite the genuine 
sensory points S a , S b9 S C9 Sj, S e into the groups spoken 
of above as essential for the so-called perception of space. 
In the point S x of the figure two true sensory points are 
grouped together, S a and S b . One of these, S b9 is also 



184 HUMAN BEHAVIOR 

grouped with S c in the quasi-sensory point S y . All three, 
*S a , S (n S cs are united in the quasi-sensory point S p . From 
eachjof the points S x , S y , S p a definite chain of neurons, 
not given in the figure, leads to a definite motor outlet. 
Suppose, now, that three other sensory points are united 
in another quasi-sensory point Sp* (not shown in the figure), 
three others in S p » 9 etc., and that from all these quasi- 
sensory points S pi S P ', Sp», etc., the excitation is carried 
to the same motor point Mp. Thus group stimulation 
of a particular geometrical design, though occurring now 
here, now there on the sensitive surface, can by way of 
Sp, Sp', S P », etc., lead to the same motor response at Mp. 
Only this question is left, whether we have the right to 
assume that by both inheritance and experience, neuron 
connections like those of Figure 47 can exist. 

As to inheritance, observation of the reactions of young 
animals as well as infants proves that we have this right. 
The present writer has repeatedly observed that children 
a few months old, with no experience whatsoever as to 
danger from animals, reacted definitely and strongly with 
shrinking, tension of the facial muscles, and crying when 
shown the face of a stuffed puppet representing a little 




Fig. 48 — Spatial stimulation with inherited response. 

pig of simple features like those of Figure 48. Since the 
reaction was the same in the case of different children and 
of somewhat different puppets, the conclusion is to be 
drawn that it was a reaction to the common features of 



INHERITED RESPONSE TO FORM 185 

these puppets, consisting in a circular head, two conspi- 
cuous circles within, the eyes, and a conspicuous triangle, 
the snout, as shown in. the figure. Obviously, then, the sen- 
sory points of the child's eyes are by inheritance combined 
into a large number, perhaps thousands, of groups so that 
all the points stimulated by an appearance, in upright 
position, more or less like that of Figure 48, send their 
excitations to a single motor point or a single central 
point whence the flux is redistributed to cause the definite 
reactions mentioned. There are probably also many other 
kinds of such groups, of other shapes, inherited by each 
individual of the human and animal race. In animals, 
too, similar definite reactions to the appearance of an 
object never experienced before have been reported by 
various observers. 

The other question is whether a grouping of sensory 
points like that of the diagram of Figure 47 and the further 
grouping (above mentioned) of such points as S p , S p r, S p », 
mentioned above as serving the same geometrical design 
on the sensitive surface, can be acquired during life. For 
this it is merely necessary that when a definite group of 
the sensory points on the retina or skin is stimulated by 
an object, a definite motor response is strongly called forth 
by a certain additional property of the same object or by 
any other property of the total situation. If this is the 
case, the nervous processes, in accordance with the law 
of deflection, must all be drawn into a single channel, the 
one leading to the motor response just referred to. That 
is, somewhere within the nervous system, they must all 
be united, as processes coming from S a , S b , and S c may be 
united in S P . Now, the next moment, the same object 
may stimulate other sensory points, partly identical with 
or entirely different from the former. What enormously 
simplifies the whole problem is the fact that of all the 



186 HUMAN BEHAVIOR 

groups which might be stimulated by the same object, only 
those relatively few are ever likely to be stimulated which 
are displaced without any rotation, like the triangles in 
Figure 46. This new stimulation by the same object may 
result from either a movement of the object or a movement 
of the eyes or of the whole body. The objects which move 
are usually animals, moving over the ground without 
rotating around any horizontal axis within their body. 
Accordingly, their images on our retina do not suffer any 
rotation. If it is our body that moves, it does not rotate 
either, nor do our eyes, so that the image is again displaced 
on the sensitive surface without any rotation to speak of. 
The flux from the sensory points now stimulated is by 
deflection carried into the same motor point. Thus a 
large number of conductor groups of low resistance leading 
to the same motor point must be established — all these 
groups having in common that the sensory points form a 
geometrical design of the same "position with respect to the verti- 
cal; for other positions could be brought about only by 
rotation around a horizontal axis, which is a relatively 
infrequent occurrence in nature. Such a response having 
once been established — or else being inherited — it can be 
varied like any simple response by further experience. 
For example, the first response of a child to fhe sight of 
a cat may be one of shrinking; later, by variation, it may 
be one of approaching and petting the animal. 

This is simple enough. The only question which might 
still be asked in order to make this kind of reaction — to 
spatial stimulation — perfectly plain, is this: Why does the 
main flux, in case S b and S c (in Figure 47) are stimulated 
together with equal intensity, pass in the direction of 
8 y ? Why does it not pass in the direction of S p as well? 
Secondly, why does it not scatter almost equally in the 
directions of »S r , S y , and S z ? To answer this question 



ACQUIRED RESPONSE TO FORM 187 

we need only refer to the law that nervous processes 
mutually attract each other. If one of them is stronger 
than the other, the result is a deflection of the weaker one 
from its course. If they are equally strong, the result is 
a union whenever the conditions of the case make a union 
of the several processes possible. Thus the two processes 
coming from S b and S C9 instead of scattering in the direc- 
tions of S X9 S y9 and S Z9 unite in the only neuron in which 
they can unite most directly, the one leading to S y9 whence 
the flux goes on directly or indirectly toward the motor 
periphery. Saying that the flux takes its path over S y9 we 
mean, as always, strictly only that the major part takes 
this path and the muscular reaction depending on S y 
overpowers all other muscular reaction. If S a is stimulated 
together with S b and S C9 the three processes can not unite 
either in S x or in S y9 but only in S p . Accordingly, the 
muscular reaction is determined by S P . That in conse- 
quence either of inheritance or of experience definite 
motor responses succeed group stimulations of a particular 
geometrical design, is thus made plain on the basis of 
our general assumptions. 

Another one among the peculiarities of the so-to-speak 
sensory aspect of nervous function, of much interest to 
the psychologist because of its significance for the theory 
of esthetics, is the perception of melody and harmony in 
music. Certain tones, affecting the ear either in succes- 
sion or in simultaneity, bring about motor reactions like 
those which generally, in any division of sense, are the 
effect of stimulations of similar kind — similar in a greater 
or lesser degree. Neglecting the fact that these reactions 
to music are chiefly emotional — to the question what 
emotional means we shall return later — we may use here 
the following quite possible and very concrete example. 
That the example is not taken from every one's daily 



188 HUMAN BEHAVIOR 

experience may be excused by the fact that common behav- 
ior hardly ever contains any unemotional reaction upon 
musical tones. Suppose somebody has been trained to per- 
form a particular responsive act whenever he hears the 
same tone twice with a short time interval between. The 
responsive act may consist in his saying simply "same 
tone" or "the tones are alike." We notice that he re- 
sponds in this particular way frequently even when the 
second tone is an octave of the first, and also, though 
less frequently, when the second tone is a fifth of the 
first. Obviously, then, the nervous flux of the octave is, 
not identical with, but similar to that of the first tone 
stimulation; and the nervous flux of the fifth is also sim- 
ilar, though in a lesser degree, to that of the first tone 
stimulation. 

If the first tone had been one of, say, four hundred 
vibrations and the second tone one of four hundred and 
five, it would not appear strange that the second nervous 
excitation should have affected the nervous system like 
the first. On an earlier page we spoke of the specific 
resistance of neurons. It goes without saying that any 
neuron having a specific resistance for the flux which is 
caused by the auditory sensory points being jerked four 
hundred times in a second, has this specific resistance also 
for a flux caused by slightly more, or less, frequently 
occurring jerks. But here observation teaches us that 
one neuron must apply the same specific resistance 
to a flux caused by jerks occurring in the ear twice ("oc- 
tave") or one and a half times ("fifth") as frequently, 
— only in various degrees with various ratios. Rejecting 
all speculation on this point, we are compelled to accept 
the bare fact that with respect to the specific resistance 
of a neuron a simple ratio of jerks can take the place of a 
near number of jerks in the auditory organ. A full know- 



MUSIC 189 

ledge of the chemistry of the nervous flux may in the future 
make the evident fact plain to our understanding. 

It does not follow, however, that in every neuron with- 
out exception a simple ratio must have this effect. On the 
contrary, there is good reason to believe that only a minori- 
ty of all the neurons connected with the ear function thus, 
for there are even people — those who are entirely unmu- 
sical — in whom practically no "ratio" reactions of this kind 
are found, who, we may assume, possess no neurons what- 
soever of this vicarious function. In infancy, too, this 
function in auditory excitation seems to appear later than 
the other, so that we may regard it as a comparatively re- 
cent acquisition of the race. Now, if all the neurons do not 
apply their specific resistances to simple-ratio stimulation 
of the ear equally as to near-number stimulation, the sub- 
ject's ultimate motor response, the muscular reaction 
proper, need not be identical in every case of similar and 
of simple-ratio stimulation of the auditory organ. An 
example will show what conditions are favorable to a re- 
sponse of this sort, — the nature of the just preceding reac- 
tion especially. Let a tone and its octave stimulate a 
person's auditory organ. Suppose that, a fraction of a 
minute before, many of those neurons have carried exci- 
tations which do not apply their specific excitations to 
simple-ratio stimulations of the ear : — two slightly mistuned 
tones may just have affected the ear. Then these neurons 
owing to their recent functioning, rather than the others, 
will function now again and the motor reaction to the two 
tones must be the usual one to two "tones quite different, " 
because of their difference in the number of jerks. Our 
general explanation of that property of the nervous sys- 
tem which is the basis of all music (of melody and har- 
mony) by no means involves us — as one might fear — in the 
difficulty that the motor reaction to tones of a simple 



190 HUMAN BEHAVIOR 

ratio of vibration rate must inevitably be always the 
same as the motor reaction to tones of similar vibration 
rate. 

No attempt will be made here to answer the question 
as to the origin of the fact that a limited number of the 
neurons of the human nervous system apply their specific 
resistance in various degrees to a variety of auditory nervous 
processes provided that the frequencies of the jerks re- 
ceived by the ear form certain simple ratios. Too much 
printer's ink has already been wasted on proposed answers 
to this question, of which none appears thus far entirely 
plausible. 

_A third peculiarity of the sensory aspect of nervous func- 
tion, which we shall discuss here, is the rhythm which is 
often observable — not in animals but in man — in the mo- 
tor reactions when the stimuli occur at fairly regular inter- 
vals but without being combined into any groups by phys- 
ical accentuation, objectively. We mean by rhythm the 
subjective grouping, the fact that a definite, unitary re- 
sponse corresponds, not simply to each single stimulus, 
but rather to a group of stimuli, — this group recurring 
in the sensori-motor activity with regularity for some time. 

Take this example. I am sitting at the open window 
through which the regularly recurring puffs of a distant 
steam engine reach my ear. Suddenly I am imagining 
the strains of a waltz. The puffs of the engine seem to 
turn into the successive chords of the music and, at the 
same time, seem to have lost their former absolute regulari- 
ty. They incite me to beat with my hand; but the move- 
ments of the hand are not all equal. Six of them fall into 
a group, and this group again consists of two parts of three 
beats each. The first of the six beats is executed with 
great vigor and mainly from the shoulder joint. The 
following two are executed with a much weaker movement 



RHYTHM 191 

of the hand, and then too, the upper arm takes 
hardly any part in the motion, which occurs from the 
elbow joint rather, or even merely from the wrist. The 
total time occupied by these two beats is slightly less than 
double the time of the first beat. The fourth beat (the 
first of the second part) is comparable to the first of the 
group, but has the same properties in a slightly lesser de- 
gree. The fifth and sixth are comparable to the second and 
third. We call this the perception of rhythm — of a 
particular rhythm in this particular case. How do I 
come to be affected in this peculiar way by absolutely 
regular puffs of a steam engine? 

This habit of reacting is acquired by each individual in 
innumerable different ways. Let us at once give a concrete 
example. Imagine a gardener having planted a double 
row of plants like the stars of Figure 49. In order to keep 



Fig. 49 — How the habit of rhythm may be acquired. 

the loose earth, just thrown around the roots of each plant, 
from drying, it is necessary to compress it and thus render 
effective the capillary attraction which draws the mois- 
ture from the lower soil. The quickest way of doing 
the work is to walk along the center line of the double row 
and to step, with the full weight of the body, on each of 
the places which need compression, using, of course, 
alternately the right and the left foot. Now, try to 
walk ahead, doing this, and observe how your legs most 
naturally act during this procedure. While you are 
standing on your right foot, the muscles of your right leg 
are strained in such a way as to keep the leg straight and 
able to support the weight of the body, but not in such a 



192 HUMAN BEHAVIOR 

way as to throw readily the weight of the body upon the 
other foot. For this a complete readjustment of the mus- 
cles of the right leg is requisite. To bring about the 
muscular readjustment, you most naturally let the body 
fall lightly upon the left foot and let it swing back to the 
right. Thus you assume that new position on the right 
foot in w^hich the tension of the various muscles is ad- 
justed so that the full weight of the body can be thrown 
on the left foot forcefully and skillfully. The left foot 
now hits exactly the spot in the left row on the ground 
where the compression of the soil is needed. 

What, then have you really done instead of stepping 
simply from the right foot upon the left? You have made 
two intermediate steps of a much less forceful kind, merely 
preparatory to the proper stepping on the loose soil. Be- 
fore you now step on the next spot in the right row, you 
make again two preparatory steps, and so you continue 
your agricultural work most easily (that is, most naturally) 
and most effectively. Between each two compressing 
movements there are always two different preparatory 
movements, both of an easy character. Why just two 
different preparatory movements? Obviously because 
man is a symmetrically built and two-legged animal. If 
man were built like a horse, the total muscular activity 
might, and probably would, be rather different. Surely, 
if man were a three-cornered animal, the case would be 
entirely different, — most probably he would not even have 
any tendency then to plant his garden in double rows. 

One must not think that all this cannot have much signi- 
ficance for rhythm, since most people who have rhythm 
have never planted any garden in the way indicated. This 
is true. The one example* of human activity was only to 
show t hat the activities of man in general tend to be habit- 
ually k of such a nature that the main motion is preceded 



GROUP ACTIVITY 193 

by a double or single (example below) preparatory 
movement of a less forceful kind. Thus the human nervous 
system becomes accustomed to muscular innervations 
arranging themselves in a group of three (or two) successive 
innervations of which one is strong. The individual 
possessor of the nervous system then has the habit of 
performing group activities rather than entirely uniform 
motions which follow each other like the puffs of an engine. 
He may then be said to have the habit of rhythmical 
perception, that is, the habit of reacting by a group activity 
to a series of perfectly uniform stimulations like our series 
of puffs, which directly, by their objective properties, in no 
way incite any group activity. That animals do not acquire 
any such habit of rhythm is readily understood if we only 
consider that horses or dogs do not habitually perform any 
systematic labor at all comparable to that mentioned above 
of a gardener. But in man's life systematic labor plays 
an important part — and not only labor, but also systematic 
play, like dancing a waltz. When the nervous system 
has once thoroughly acquired the habit of a particular 
group activity, this activity may by a " variation of re- 
sponse" quite readily show itself in a part of the body 
where it was not, and in a motion in which it was not, 
acquired, as when I beat with my hand the rhythm of a 
waltz while my feet are at rest. It may by a further 
variation of response result in my naming an auditory 
impression as when, in reply to a certain question, I speak 
or write: "This is a waltz," without having in the least 
had recourse to counting up to three, the distinguishing 
number of that rhythm. 

Our example of the gardener illustrated the acquisition 
of the habit of triplet activity. We have also referred to 
the existence of the habit of doubled activity. If we 
are permitted to take our example again from agricultural 



194 HUMAN BEHAVIOR 

work it is still easier to find examples in the shop 
or factory — we may imagine a gardener who has planted 
a single line of plants and has now to compress the 
soil at the successive spots. Suppose he does this 
with his left foot. He must then make before each 
compressing movement of the left leg one preparatory 
movement of the right leg (or three if he chooses, 
one of the right, one of the left, and one again of the right 
leg) in order to assume the proper position to the right 
of each plant. We thus have one weaker muscular 
innervation between each two of the main innerva- 
tions, a group activity composed of two motions, one 
strong, one w r eak. 

Our most common rhythmical perceptions are of the 
doublet and triplet kind. There are also familiar rhythms 
composed of four, six, eight, twelve, and sixteen units. 
These are simply compounds of doublets and triplets. 
For example, a group of twelve is a doublet of six, and 
this group of six again is a doublet of three; or the 
group of twelve may be a triplet of four, etc. We are very 
familiar with such groups in dancing. It is a common, but 
on that account no more correct, belief that people dance 
because of an inherited " sense of rhythm, " a special instinct 
which impels them to perform group movements of two, 
three, four, six, eight, etc., elements. The truth seems to 
be rather that w r e have a sense of rhythm because we dance 
than the reverse, that we dance because of an instinct 
of rhythm. Dancing is a group activity of our muscles 
which is easily learned because of its relative simplicity 
and its adaptation to the human anatomy. Since this 
activity is so easily learned and performed, it is used for 
sport, for play. Thus it becomes one of the sources of the 
general habits of rhythm. 

All common rhythms are reducible to doublets and trip- 



NOT INSTINCT, BUT HABIT 195 

lets by division with two or three. There is nothing mys- 
terious in the fact that groups of five, seven, or nine units 
are not common rhythms. This is merely the conse- 
quence of the fact that systematic labor or play does not 
readily employ the human body with its two hands and 
two feet in such a way as to lead to the acquisition of a 
habit of combining, say, four different weak, preparatory 
motions with a strong, fifth motion into a single group. 
If one invents a certain playful activity of five or seven 
elementary motions — one of them being strong, the rest 
serving as different preparatory movements — and exercises 
it until it becomes perfectly habitual, he acquires a rhyth- 
mical perception of a quintuplet or of a septuplet which 
appears no less natural and quasi-inborn than the rhyth- 
mical perceptions of a triplet and doublet. Such has been 
the present writer's personal experience. 

Let us understand, then, that the so-called "percep- 
tion" as well as the execution of rhythm, as a nervous 
function, is simply successive group activity, involving 
in each case the successive innervation of a definite num- 
ber of different muscle sets. One reason why in the text- 
books rhythm is so shrouded in mystery is clearly this, 
that it is usually thought of as an instinctive nervous 
reaction to number instead of being regarded as a (numeri- 
cal) habitual group of successive sensori-motor activities 
unified by their leading to a single end. Number enters 
into such a function really only as a conception of the 
scientist who describes it, not of him in whom the func- 
tion occurs. 



FIFTEENTH LECTURE 

Imitation. Auditory and visual imitation at different 
stages of life. Kinesthetic imitation not inherited; of little 
importance even tvhen acquired. Emotional reactions. 
Either contraction or relaxation prevailing in either organic 
or skeletal muscles. Emotional reactions inherited. Emo- 
tional reactions either of direct or of indirect value, for 
example, as signals for social interaction; especially in 
primitive man and in animals. Civilized man, deriving 
little benefit from his emotional reactions, practically unable 
to control them by experience. 

WHILE discussing speech we had to men- 
tion the fact that certain activities of 
the speech organs occurring in response 
to auditory stimuli have the peculiarity 
of bringing about sounds very much like those which 
served as stimuli in the first place. In any such case 
where the motor response repeats the stimulation we speak 
of imitation. "Imitation," therefore, is not the name of a 
force, but of a mode of reaction. Here the subject has 
imitated the sound heard . But imitation, of course, is not 
restricted to auditory stimulation. In auditory stimula- 
tion it makes its first appearance as one of the great 
factors of human education, — during the second year of 
life. Visual imitation attains its maximum of importance 
about a year later. While auditory imitation plays a 
part of ever decreasing significance as life advances, 

196 



AUDITORY AND VISUAL IMITATION 197 

visual imitation determines our actions in all stages of 
life. The infant imitates the speech sounds which are 
produced by children and older people in his presence. 
The eight or ten year old child has almost ceased to 
imitate the speech of others. How slight the tendency 
to imitate speech has become in grown people, all those 
know from experience, to their regret, who have ever 
learned or taught a foreign language. Grown people 
will do a hundred other things rather than repeat over 
and over again a phrase just heard, as small children do, 
— the secret of children's rapid success. It is quite 
natural, however, that auditory imitation is so strong 
during the second and the following few years and so weak 
later. The child must learn to speak early in life, and he 
learns by imitation. When this is once accomplished, 
imitation is no longer necessary. Aside from learning, 
auditory imitation has no value of its own. With visual 
imitation the case is quite different. It is true that a 
good many skillful movements may be and are learned 
by visual imitation; however, the imitative act itself, aside 
from all learning, has an enormous biological value all 
through life, in old age no less than in middle age and 
infancy. When we see a crowd gather on the street, we 
immediately run to the spot ourselves, — not because we 
still have to learn how to run to a point seen, but because 
it is of immense value for our social life to do at any time 
what we see other people do, exceptions notwithstanding. 
There can hardly be any doubt that auditory imitation 
is largely the result of inheritance. All the elementary 
sounds are imitated because the necessary paths of small 
resistance are inherited. The apes, having practically 
the same vocal organs, do not, in our zoological gardens, 
acquire human speech, obviously because this factor of 
nervous inheritance is lacking. One might argue that 



198 HUMAN BEHAVIOR 

the existence of the so-called "baby talk" demonstrates 
the importance of experience in auditory imitation. It 
is true that baby talk is the result of the child's experience, 
not of his inheritance. But baby talk is not acquired by 
imitation on the child's part. The infant babbles in 
response to all kinds of stimulations, auditory or not 
auditory. The sounds thus produced are imitated by the 
parents and used by them in the baby's presence with 
reference to particular situations. The child then learns, 
by this experience, the meaning created by his parents 
for these sounds, which are in the main reduplications; 
that is, he learns to use these simple words in these particu- 
lar situations, — by imitation on the part of his parents. 
Thus he acquires the talk peculiar to the nursery. It is 
clear, then, that the existence of baby talk is no argument 
in favor of any importance of experience in auditory 
imitation. Inheritance brings about adequately the 
imitation of all elementary speech sounds. To combine 
these elements into complicated groups composed of 
many successive elementary sounds, requires indeed 
both experience and reflex imitation on the child's part, 
— we have studied the process in a previous lecture. The 
imitation of the elementary sounds, however, is regulated 
by inherited reflexes. 

In visual imitation, on the other hand, there seems to 
be little dependence on special inherited reflexes. Even 
the simplest movements which are executed by visual 
imitation seem to depend on experience. We have dis- 
cussed in an earlier chapter the simplest reflex movements 
of the hands and feet. There is in them no imitation of 
any movement seen. Only when the child begins to 
make new movements by experience, can imitation be 
observed. And even in these earliest movements learned 
by experience there is hardly any imitation. The child 



EXPERIENCE IN IMITATION 199 

learns, for example, the upward movement of his hands 
which we make in order to take a thing from a shelf above, 
— but not by imitation, as we have found. He learns to 
creep, to stand, to walk, but not by imitation. It is only 
after he has acquired these skillful movements of his 
hands and feet, that visual imitation becomes conspicuous. 
Now we observe that the little child, barely able to walk, 
joins us when we are standing with our back against the 
wall and takes his place at our side, leaning his back 
likewise against the wall. Now he puts his hat on when 
we put our hat on. Now he places an open book on the 
music stand of the piano before he strikes the keys with 
his little fingers, because he has seen us open our music 
before striking the keys with our fingers. Visual imita- 
tion, therefore, depends altogether, or practically alto- 
gether, on experience; there is scarcely any inherited visual 
imitation. 

We have discussed auditory imitation and visual 
imitation. Shall we add, as a third important class, 
kinesthetic imitation? If we apply the term imitation 
to every sensori-motor process which brings about directly 
a repetition of its stimulation, we might speak also of 
kinesthetic imitation. But whoever would restrict the 
term to cases where the stimulation results from an 
extra-corporeal (visible or audible) phenomenon, should 
not use this phrase, for kinesthetic stimuli are not external, 
but physiological phenomena. He might then, instead 
of adding a third class of imitation, speak of circular 
sensori-motor processes. In an earlier chapter we have 
already had occasion to mention that circular reactions 
are of much importance in the acquisition of skillful 
movements because they hasten, through repetition of 
the same nervous activity, the establishment of paths of 
low resistance. The question which interests us here is 



200 HUMAN BEHAVIOR 

this: Is kinesthetic imitation, if we are permitted to 
apply the term, largely inherited? 

One might think that the inheritance of kinesthetic 
imitation, of the occurrence of the motor response in the 
very muscles in which the sensory excitation occurred, 
is self-evident from the nature of the case, for two reasons. 
Did we not state the great importance of kinesthetic 
excitation for habits of temporally complex, that is, of 
serial, reactions? Secondly, should not nervous connec- 
tions of low resistance be inherited between sensory 
points and motor points located side by side in the body, 
when many such connections are inherited between widely 
separated sensory points and motor points? Both these 
are false arguments. As to the latter, it is clear enough 
that in the lowest organisms, having no nervous system, 
the motor response occurs primarily at the point itself 
which has received the stimulation. It does not follow, 
however, that after differentiation of the tissues the sensory 
and motor points, because they are originally identical, 
must be closely connected by nervous paths. It is true 
that in the peripheral parts of the body the sensory and 
motor neurons of the same region usually run parallel in 
big bundles, the so-called nerves. But within the central 
nervous system they separate; and they are connected 
to form short reflex arches only where the functional needs 
of the organism unite them, as in the case of all other 
sensory and motor neurons. The former argument has 
no greater strength. Not everything of great importance 
is necessarily inherited. Further, in so far as kinesthetic 
excitation plays a part in the execution of habitual serial 
reactions, we have no imitation, for each kinesthetic 
stimulation in a serial reaction brings about a contraction 
of a new set of muscles, and a different kinesthetic stimu- 
lation. On the other hand, where we have repetition of 



NO KINESTHETIC IMITATION 201 

a truly inherited sensori-motor process, we have imitation, 
but it is not kinesthetic. For example, when a child 
learns to pile up blocks, (compare Lectures 11 and 12) 
there is a circular reaction, — imitation in so far as the 
child imitates a model (a block standing) by creating a 
thing like it ( a block or pile of blocks standing) ; but the 
stimulation of the circular process is visual, not kinesthetic. 
Far from admitting, then, that kinesthetic imitation is 
largely inherited, we are led to deny almost its very 
existence, even as acquired by experience. Indeed, if it 
were inherited, it would greatly retard the acquisition of 
useful habits of reaction. For example, the child, instead 
of learning how to build a house of blocks, would continue, 
through the influence of such imitation, to move his hand 
up and down in the same manner without being influenced 
by the fact that blocks other than the one in his hand 
are lying about. Kinesthetic imitation, if inherited, would 
reduce man's biological significance to something like 
that of mechanical toys in a child's world, capable 
only of performing the same jump in endless repetition. 
There is little probability, then, that such a function 
should be acquired during life. Kinesthetic excitation as 
a biological factor seems to be confined to serial motor 
activity, consisting in a succession of different acts; there, 
indeed, kinesthetic excitation is indispensable. 

While the larger part of the motor activity of an animal 
consists of reactions upon the objects of the environment, 
brings about, indeed, in the case of visual or auditory 
imitation, a duplication of an environmental phenomenon, 
there are also motor activities which do not seem to affect 
the objects of the environment at all, and directly, most 
certainly, do not affect them; which are confined to the 
inner world of the organism. Motor responses of this 
class are often called emotional reactions. There is an 



202 HUMAN BEHAVIOR 

enormous literature debating the question what the 
emotions are aside from these internal reactions of the 
organism, what they are as purely introspective pheno- 
mena. Let us be satisfied with the simple statement 
that in most, if not all, conditions of animal life which are 
called emotional, internal reactions occur; and let us, 
without entering into a discussion of introspective "emo- 
tions," give a broad classification of them and a brief 
discussion of their biological significance. 

In order to understand these internal reactions properly, 
we have to discuss not only muscular contraction, but also 
muscular relaxation, and to regard the latter as a factor 
as positive as the former. Lacking space, we cannot 
here, and need not for our present purpose, enter into a 
discussion of the physiological mechanism by which relaxa- 
tion as well as contraction is brought about. Let us 
regard either simply as the motor response to a proper 
excitation of sensory points. We have then at once two 
large classes of internal reactions, according as relaxation 
or contraction of the internal organs dominates, — we say 
"dominates" as it is entirely possible that relaxation of 
some organs be accompanied by contraction in others. 
A subdivision of each of these classes is found by reference 
to the two classes of muscles in our body, the "organic" 
muscles which perform the mechanical work of our internal 
organs, and the skeletal muscles which control the position 
of the members of the body, relative to each other, and 
their motion. The important fact that in the large 
majority of all eases of reaction in the organic muscles 
react ions in the skeletal muscles occur simultaneously, 
i- comprehensible enough. In general, whenever the 
skeletal muscles tend more than ordinarily to relax, the 
motion of the body will be unusually weak; and whenever 
the skeletal muscles tend more than ordinarily to contract, 



EMOTIONAL REACTIONS 203 

the motion of the body will be unusually vigorous. Thus 
we should obtain among those motor responses with which 
we are at present concerned, four main classes : (1) Relaxa- 
tion of organic muscles combined with vigorous motion. 
(2) Contraction of organic muscles combined with vigorous 
motion. (3) Relaxation of organic muscles combined 
with weak motion. (4) Contraction of organic muscles 
combined with weak motion. It is to be understood, 
however, that in no case do we include all the organic 
muscles or all the possible motion of the members of the 
body. Let us see, now, to what extent this classification 
aids us in characterizing familiar types of emotional 
reaction in animals and in man. 

Unusual contraction or relaxation of the organic muscles 
becomes apparent chiefly in the blood vessels, the heart, 
the stomach, the intestine, the bladder, and the skin. 
If the ring-shaped muscles of the smaller blood vessels 
relax, the vessels take up a larger amount of blood forced 
into them by the heart. The skin, containing innumerable 
small blood vessels, then looks red. Our first class, there- 
fore, is illustrated by a person who looks red, whose skin 
is warm owing to the presence of a large quantity of 
warm blood, and whose motion is very vigorous. We 
recognize in him what we commonly call the emotion of 
joy or the emotion of anger. Whether we apply the one 
or the other name, depends on the special situation, which 
may call forth — so far as the skeletal muscles are con- 
cerned — either movements of dancing, shouting, clapping 
the hands, and the like, or movements of attack. That 
the sensory excitation caused by the situation affects not 
only the skeletal muscles, but also such muscles as those 
in the walls of the blood vessels, is, by the way, a good 
illustration of the fact which we have previously emphasiz- 
ed, namely, that our nervous system is one, in spite of the 






204 HUMAN BEHAVIOR 

special physiological and anatomical names applied for 
various reasons to its parts. This unity of the nervous 
system can also be demonstrated by such a simple experi- 
ment as this. Address a person suddenly with the ques- 
tion, "Why do you blush?" The response will consist, 
of course, in words spoken; but in addition, frequently, 
the person will be observed to blush, although ordinarily 
stimulation of the auditory organ is not capable of causing 
a relaxation of the muscles in the blood vessels of the face. 
The situation in question, in which we find that person 
who looks red, etc., probably causes activities of the skel- 
etal muscles which are of a direct objective purpose, for 
example, running. But it causes also activities of the 
skeletal muscles which are of no direct purpose, for 
example, the tension of the facial muscles, the grinning, 
of a person in joy or rage, often represented by carica- 
tures like Figure 50. Since all the muscular functions 
with which we are concerned at present, are inherited, 
not acquired by experience, we may ask how we can 
understand the evolution of such seemingly useless reflexes. 
That in anger, where an animal attacks another animal, 
or in joy, where an animal applies to good use an object 
which he has succeeded in obtaining, vigorous motion is 
biologically of great value, is self-evident. But of what 
use is grinning? 




Pig. 50 — Tension of the facial muscles in joy or anger. 

One answer to the question is this. In anger, grinning 
may mean simply getting ready to bite, for the mouth is 



JOY AND ANGER 205 

an important weapon of attack of animals and of primitive 
man; and in joy, since the most important article applied 
to good use is an article of food, grinning may mean simply 
getting ready to bite off and chew. But it may have still 
another biological meaning. It may be of indirect value 
by helping to bring about social interaction — positive or 
negative, friendly or hostile — through rendering the 
situation quickly understood by other members of the 
animal species. 

Let us give further examples to illustrate the in- 
direct, purely social, value of movements or attitudes. 
In an infant the stimulation of hunger may cause reflex 
movements of the hands upwards, with the result that 
the fingers get into the mouth and are sucked, or that the 
finger nails, when the hands are withdrawn, scratch the 
face. Although these results are directly without any 
value to the child, they are indirectly of the very greatest 
value, for their sight stimulates the parents to definite 
activities, for instance, to providing the necessary food 
for the baby. A mother describing these reactions would 
surely say that the baby is "so hungry that he tries to 
put his hands into his mouth," or "so angry at the delay of 
his dinner that he scratches himself. " This social value is 
not the least significant explanation of the evolution of 
reflexes which are directly of little value. There is still 
left to explain why in situations of joy or anger the blood 
should rush into the skin. Perhaps this is merely a symp- 
tom of the unusually strong circulation of the blood through 
the whole body, useful for continued activity of the 
muscles which, for physiological reasons, would soon be 
incapacitated for work without being washed out con- 
stantly by the blood current. But the redness of the 
skin, just as the tension of the facial muscles, the grinning, 
has also an indirect value of much importance, a value for 
social interaction. A red-faced man in a given situation 



206 HUMAN BEHAVIOR 

causes the situation to impress other men in a way by no 
means identical with the way in which they are affected 
by the situation while the man in its center looks pale. 

The second class of these peculiar motor responses was 
distinguished by contraction of organic muscles combined 
wit h vigorous motion. We recognize the symptoms of what 
is called the emotion of fear. That the stomach, the 
intestine, the bladder, and other internal organs contract 
in a fearful situation, that the heart beats with unusual 
force, is a familiar fact. Contraction of the smaller blood 
vessels causes the blood to disappear from the skin and 
the latter to become pale. Contraction of the minute 
muscle fibers distributed all through the skin, gives it 
the appearance ordinarily called "goose flesh"; and where 
the skin is hairy, this contraction causes the hair to "stand 
on end." The skin, having lost its blood, cools off, and 
this cooling in turn calls forth reflexly shivering, the 
ordinary physiological response to cooling of the skin. 
The vigorous motion, adapted to the particular situation, 
shows itself in the individual's running faster than he is 
ordinarily able to. Vigorous motion, however, is only 
one external symptom of an extraordinary tendency to 
contract. Some degrees further, and th's tendency results 
in a cataleptic state, a continuous contraction of all 
muscles, making all motion impossible. One person or 
animal responds to a dangerous situation by running, 
another is "turned into stone." 

If we now ask of what biological value these inherited 
reactions are, we find the answer very readily so far as 
the extraordinary tendency of the skeletal muscles to 
contract in response to a dangerous situation is concerned. 
The faster the animal runs away from the dangerous 
situation, the safer it is. On the other hand, if the mus- 
cular contraction progresses up to the cataleptic, perfectly 



FEAR 207 

motionless, state of the body, the animal is again relatively 
safe in case the danger comes from another animal being 
in the neighborhood, owing to the fact that a motionless 
body is less readily perceived by the eye — not to speak 
at all of the ear — than a moving body. Many species of 
birds and small mammals can be observed to assume this 
motionless attitude when surprised by a man or a hostile 
animal, especially when the dangerous being is not yet so 
near that the exposed animal is within direct reach. Many 
a hunted animal escapes the hunter by this mode of reflex 
reaction. 

Why the organic muscles should tend to contract, 
however, is less clear. Apparently, their contraction in a 
dangerous situation can be of no direct value. A certain 
amount of indirect value, on the other hand, with respect 
to social interaction, is obvious, especially when the ex- 
posed animal is in the cataleptic state. The skin having 
lost its blood, the exposed animal resembles more nearly 
a dead animal; and this resemblance may save it. For 
example, it is reported that certain bears will leave a 
seemingly dead man's body unmolested; not to reiterate 
the anecdotes of hunters who gave no attention to an 
animal whose possession they felt sure of, because it was 
already dead, but who discovered suddenly that it had run 
away. Even an animal being chased by another may 
appear more formidable than it really is, on account of its 
fur or feathers standing on end, or may retard the enemy 
by the ejection of disgusting substances. 

Our third class of responses was distinguished by relaxa- 
tion of organic muscles combined with weak motion. 
This is of all the four classes the least important one. We 
experience it after having eaten a hearty dinner, — but this 
is not everyone 's habitual occupation. Of vast importance 
is the fourth class, distinguished by contraction of organic 



208 HUMAN BEHAVIOR 

muscles combined with weak motion. It is exactly the 
opposite of the first class (joy) and is, indeed, the reaction 
to any kind of disappointment, — what we most commonly 
call the emotion of sorrow. We can at once derive the 
symptoms and comprehend the biological value of this 
reaction if we recall that in animal life and in the life 
of primitive man the most ordinary kind of disappoint- 
ment consists in the want of food. Imagine a winter 
month: every article which might serve as food covered 
by snow and impossible to find, for weeks or longer, until 
the weather changes. An animal which, under these 
circumstances, would continue to run about for food, 
would soon fall dead from exhaustion. However adverse 
the situation, the body can survive living on the sub- 
stances stored away in its own tissues, if it only consumes 
this limited supply economically. For this the first 
requirement is that all muscular activity be reduced to a 
minimum. Thus we understand why the nervous system, 
in a disappointing situation, tends to leave the skeletal 
muscles in a state of relaxation. A person in great sorrow 
is so far from being master of his skeletal muscles that 
he drops as if he were completely paralyzed, like Romeo 
in Friar Laurence 's cell : 

" Wert thou as young as I, Juliet thy love, 

An hour but married, Tybalt murdered, 

Doting like me, and like me banished, 

Then mightst thou speak, then mightst thou tear thy 
hair, 

And fall upon the ground, as I do now, 

Taking the measure of an unmade grave." 
A disappointed person looks like Figure 51 (the opposite 
of Figure 50), since the relaxation of the facial muscles 
causes the angles of the mouth to be pulled down by the 
weight of the lower jaw. 



DISAPPOINTMENT 209 

Why should the nervous system, in a disappointing 
situation, tend to cause contraction of the organic muscles? 
Recall the animal just spoken of, disappointed in its food 
supply. If it does not exercise its muscles, little or no 
heat is produced, for the skeletal muscles are, physiologi- 
cally, the very furnaces of the body. If little heat is 
produced, the loss of heat must be safeguarded against. 
Thus the biological value of the contraction of the muscles 
in the walls of the blood vessels becomes evident. The 




Fig. 51 — Relaxation of facial muscles in disappointment. 

contraction of the vessels prevents the blood from circu- 
lating much in the periphery of the body where cooling 
mainly takes place. The cooling by the conduction of 
heat through the tissues covering the body is little to be 
feared as long as the w^arm blood is kept in the inner parts 
of the body and prevented from circulating through the 
periphery. The actual cooling of the skin, exciting the 
sensory points of the skin, causes the reflex and habitual 
response of the animal's seeking shelter, again reducing 
the loss of heat, of physiological energy. Thus con- 
traction of the organic muscles keeps the animal alive 
until a change of the external conditions enables it to 
resume its ordinary manner of life. 

Less plain than these reflexes seems the fact that 
often a disappointed person weeps. From our 
statements thus far one should rather expect a person in 
joy to weep, provided we derive weeping from an unusual 



210 HUMAN BEHAVIOR 

blood pressure in the lacrimal glands, an unusual fulness 
of the blood vessels owing to the relaxation of the organic 
muscles. Indeed, people weep when joy reaches a high 
degree. That people weep in disappointment becomes 
plain when we recall the generally accepted notion that 
weeping gives relief from excessive sorrow. Only we 
should rather say: when the nervous system, through 
normal exhaustion, commences to respond to the disap- 
pointing situation less excessively, then weeping occurs. 
The tears here are actually not a cause, but an effect of 
relief. The organic muscles, excessively contracted for 
some time, at the moment when exhaustion of the nervous 
system commences, relax completely and the blood 
pressure in the lacrimal glands suddenly rises far beyond 
the normal. 

All these responses of the organic muscles, with or 
without simultaneous activities of the skeletal muscles, 
of which we have discussed here only those which can be 
most easily classified, are the result of nervous connections 
between certain sensory and certain motor points and 
group formation among these connections, inherited by 
each individual of the species. The extent to which they 
can be modified by experience is slight, almost zero. 
This is, perhaps, to be regretted, since in the life of modern 
civilized man they have largely lost the biological useful- 
ness attributable to them under primitive conditions of 
social life. Nevertheless, however advanced the present 
evolution of man's nervous system, in his inability to 
control these responses by experience, man practically 
shares the fate of the animals. 



SIXTEENTH LECTURE 

The speech function serving as a generalizing function. 
Abstraction a kind of generalization. Advantages of the 
written language in generalization for individual use and for 
communication. Science the sum total of all generali- 
zations which mankind has tested and collected. Written 
symbols becoming a class of {artificial) objects to which 
man learns to respond as formerly he learned to respond 
alone to the objects of nature. Arithmetic. The general- 
ization "force" in mechanics: a creation of man like all 
other generalizations. Advantage of handling words 
rather than things. Danger of speculation. 

WE have already discussed speech, but 
only as an instance of temporally complex 
sensori-motor activity. We shall now 
discuss the speech function as that ner- 
vous function upon which the distinguishing .features of 
human as compared with animal life are based. Science 
is justly regarded as the chief characteristic of modern 
human life. Since generalization and abstraction are the 
foundations of science, we shall have to show by concrete 
examples what nervous activities are meant when we speak 
of generalization and abstraction. 

(1) A child, in the presence of such things as bread, fruit, 
edible roots, meat, impressing his eye, (S a , S b , S C9 S d in 
Figure 52) learns to pronounce the word "food" (M w in 
Figure 52). The nervous function is simply a variation 
of response. A new response takes the place of those 

211 



>h 



HUMAN BKIIAVIOR 



which at first succeeded these stimuli and which are indi- 
cated in the figure by the dotted lines leading to motor 
points without lettering. Instead of handling the things 




Oa Ob Oc 0(j Ow I lw 

Fig. 52 — Naming takes the place of handling. 

in accordance with his previous instincts and habits, he 
speaks the word which is used by older people as the com- 
mon name of these things. (2) On the other hand, when 
the child's ear is struck by the sound of the word "food" 
(S w in Figure 53), he learns to respond, if otherwise than 
by saying "food" (M w in Figure 53), exclusively by 




Sw Mw M e M f M g M h 

Fig. 59 — Handling takes the place of talking. 

such muscular activities as are adapted to the preparation 
for eating' of bread, fruit, edible roots, meat, and similar 
articles and to their consumption by the mouth (M e , M f , 
M gy M h ). This is also simply a variation of response. 
The word heard — in any of the nervous functions bringing 



GENERALIZATION 213 

about the responses of handling these things — takes the 
place of the things seen, indicated in the figure by the dotted 
lines starting from sensory points without lettering. From 
now on, whenever the word has struck the ear, the muscles 
which co-operate in properly handling these things get 
ready to work rather than other muscles to handle other 
things which also impress the eye at the time. The ner- 
vous paths serving the latter impressions are at a disad- 
vantage in not being "cleared for action" by the sound 
of the word exciting the ear. 

Under (1) we mentioned the speech movement enoun- 
cing the word food, under (2) the speech sound of the word 
food striking the ear. It is plain, then, since the sound of 
the word strikes also the own ear of the person enouncing 
it, that the motor response of speaking and the resulting 
excitation of the ear becomes a double link inserted between 
the mere sight of the article of food and its proper handling. 

Sight of thing ^handling 

Sight of thing hspeaking hsound of word ^handling 

This insertion of a new link into the chain of functions 
seems an unnecessary, uneconomical complication due to 
the individual's experience, so that experience in this case 
would be harmful rather than useful. It would indeed 
be an undesirable superfluity of nervous and muscular 
activity, were it not for the fact that the inserted link is 
practically the same however different the visual appear- 
ances of the articles of food — they are all called by this name 
— and however different the ways of handling and preparing 
them before putting them into the mouth — they are all 
called out by the same word food. The insertion between 
two nervous processes — let us call them A and B — of 
such a link of activity, always identical in spite of untold 
variations of A and of B, is exactly what we call, in another 



214 HUMAN BEHAVIOR 

terminology, in that of logic, generalization. All the 
visual appearances of things eatable, on the one hand, and 
all the motor responses of eating (including therein the 
necessary preparations), on the other, are held together by, 
arc, so to speak, under the command of, a single, though 
originally not quite simple, biological function of the speech 
reaction class. We understand immediately why in the 
nervous life of animals there can be little, if any, generali- 
zation since animals do not possess speech. 

Let us imagine another instance. I, being still an inex- 
perienced child, am occupying a definite position. Another 
being, animal or human, is occupying another position, 
more or less distant from mine. I have a solid article, no 
matter of what kind, in my hand, or between my teeth, 
or in a pocket, or beneath my feet. A certain stimulation 
— easily imaginable and therefore needing no definition — 
causes me to perform such a motion that the article is 
transferred from its place near me to a new place near the 
other being. While my own motion, as well as the 
article changing place, impresses my eye, or directly after 
this impression, the word "give" happens to be spoken 
in my environment. I imitate the sound and thus learn 
to respond to the situation of an article being transferred 
by my own motion from me to another being, by saying 
"give." But I also learn to respond to the auditory 
impression "give" by such a motion transferring an 
article from me to another being. Here, the sum of the 
motor excitation "give" and the sensory excitation "give" 
(briefly speaking the speech function "give") is — not, as in 
t he former case of "food," a link inserted between the plain 
sensory impression of a thing and the motor response of 
properly handling it — but a seemingly superfluous repre- 
sentative of thai whole nervous process which has as its 
issue the motion transferring an article. 



ABSTRACTION 215 

Transferring— ■ — — ^transferring continued 

Transferring — ■ — y saying "give" ^sound of "give" ^transferring continued 

This representative, accompanying its constituent, would 
indeed be an unnecessary complication of nervous activity, 
were it not for the fact that the additional function is 
practically the same however different the manner of 
motion transferring the article in question: by stretching 
out the hand, throwing, kicking, dropping from an elevated 
place, rolling down a hill side, not to mention sending 
it by a messenger, by mail, or by any other device of 
modern transportation. This establishment of a definite 
function identical in spite of untold variations of the sen- 
sori-motor activities which it represents — they are all called 
giving — is obviously also a generalization. Or, in the termi- 
nology of logic, it is an abstraction. Abstraction, then, 
is a special case of generalization — generalization, not with 
reference to objects, but with reference to relations (spatial 
transference, in the instance discussed). 

The difference between the biological functions in ordin- 
ary generalization and in this special kind of generalization, 
abstraction, might be described thus. In ordinary general- 
ization the object handled is of main significance. The 
manner of handling it is of importance only in so far as 
the object is distinguished from objects of a different class 
by the proper mode of handling it, — for example, "food" 
is an object to be eaten by the responsive animal. In 
abstraction the mode of handling is of main significance. 
The object itself is important exclusively in so far as, 
if there were no object whatsoever, no handling of it 
could have occurred. 

The purpose of our present discussion is not to give a 
lesson in logic. Our intention is to show briefly, but 
conclusively, that practically no generalization or abstrac- 
tion is possible without speech, and to make clear by con- 
crete examples what is meant biologically by such terms 



216 HUMAN HEHAVIOR 

as generalization and abstraction. In order to make the 
significance of the speech function for the nervous activity 
of the individual living body — over and above the social 
significance of speech as a mere system of signals for co- 
operation in actual labor — still clearer, let us make a third 
application to a concrete case of human life. 

A child, having had both the speech experiences above 
described of "food" and of "give," happens to meet 
another person, say, a beggar, who addresses him with the 
words "food, give." The natural consequence is, first, 
that the child looks about until his eyes are arrested by an 
article belonging to the class of "food, "say, a piece of 
bread. Then he approaches the bread and would now 
respond to its sight simply by the most firmly established 
habit, by taking and eating it, had his ears not been 
stimulated by the sound of the word "give" too. So he 
responds to the total stimulation of sound and sight by 
giving the piece of bread to the other person. Similar 
occurrences take place quite frequently in the child's life; 
but the words heard are not always only food and give. 
Now and then the address will be "food, give, hungry." 
Thus the child learns, by what we have called a variation of 
response, to react to the word "hungry" in the same way 
as to the sentence (if these two words may be called a sen- 
tence) "food, give. " He learns to react to the word hungry 
by looking about for edible things, taking hold of them, and 
transferring them to the other person. What a wealth 
of possible actions is thus placed under the control of the 
single word "hungry"! The fully experienced human 
being, hearing this word, looks about until an edible 
thing strikes his eyes. But if his eyes do not perceive 
anything eatable, other activities follow. He may put 
his hands into his pockets to search for food. He may walk 
home in order to find food there. He may open 



SIGNIFICANCE OF ABSTRACTION 217 

his chest or cabinet, take money from it, and go to the store 
where food is for sale. Or he may go out to his fields, 
cut his wheat, and store it away under the roof of a barn in 
order to be able to give food at a later time when the sound 
hungry may strike his ear again. Not having any wheat 
mature on his fields, he may take out his horses and imple- 
ments and plow r the ground on which wheat is only to be 
sown. He may attend, as a student, an agricultural college 
where he learns how T to grow wheat most successfully on 
his farm. He may vote in favor of his government spend- 
ing money for the support of such a college. Further think 
of the innumerable possible activities which make pro- 
vision for the transportation of the food from place to 
place, from the producer to the consumer! To enum- 
erate even those activities which are more directly 
controlled by the word hungry, would require a volume. 
Of the activities w T hich we have mentioned, some are 
rather remotely dependent on the abstraction "hungry". 
The more remotely they are dependent on it, the more 
numerous, of course, are the other abstractions on which 
they are also — more or less directly — dependent, so that, 
then, the actual motor response becomes more and more 
the resultant of many components, of all the activities 
controlled by all the abstractions. 

We have thus far spoken of the word "hungry" only 
as denoting a sound, stimulating the ear and controlling 
by means of the nervous paths diverging from the ear a 
vast number of highly complicated motor responses. We 
said above, that the word hungry was often heard together 
with the words food and give. At such a time it must 
have been imitated by the child in question. Thus the 
pronunciation of the word hungry has become one of 
the possible motor responses to the total situation. It is 
plain, however, that the same word, hungry, is also heard 



218 HUMAN BEHAVIOR 

in other situations, especially frequently at the time when 
the subject together with the other members of the family 
takes one of his regular daily meals. At that time the 
sensory points of the stomach are likely to be excited 
by the physiological condition which is called hunger. Ac- 
cordingly, the subject learns to say "hungry" in response 
to the sensory excitation of hunger. Whenever he res- 
ponds thus, he produces the sound of the word, and this 
sound impresses his ear. Most naturally, then, the total 
(motor and subsequently sensory) speech function of the 
word "hungry" becomes an intermediate link between 
the sensory excitation of hunger and that vast number of 
responses mentioned above, all serving, with greater or 
lesser directness, to dispel hunger not only in others but 
in himself. 

What* then, is the value of abstractions to man? They 
serve to make ready, instead of the simple reflex or in- 
stinct corresponding to the stimulation, an enormous num- 
ber of complex motor responses among which a selection is 
made by the other sensory factors of the situation and the 
motor tendencies of the abstractions belonging to them. 
This complex nervous activity, which is the distinguishing 
feature of mans life as compared with that of animals, 
is made possible by the acquisition of speech. 

In this development, now, of generalized (abstract) 
nervous functions an enormous step in advance is made 
when mankind invents script. Not only can the written 
language— except for the greater brevity of speech than of 
writing- in the functions described above almost complete- 
ly take the place of the spoken language; it can even ac- 
complish much thai is denied the spoken language. First, 
it enhances preservation of the individual's generalizations 
(including his abstractions) for his own later use. Secondly, 
it removes practically all limits of space and time from 



SPEECH AND SCRIPT 219 

communicating one individual's generalizations to other 
individuals. 

As to the preservation of any generalization for the 
individual's own use, it is plain that, as long as generaliza- 
tion is mediated only by the spoken language, it depends 
exclusively on the properties of his own nervous system. 
Just so long will the generalization persist, as a path of 
low resistance, established by the speech function, leads 
from the sensory points of, say, hunger to a common central 
point, and another one from a common central point to 
that vast number of responses previously indicated. But 
such a path of low resistance can continue to exist only 
if it is constantly re-established, so to speak; for we know 
that a path whose resistance has been lowered by individual 
experience tends to resume gradually its original high 
resistance. After the individual has acquired — by a simple 
variation of response — to the sight of the written word the 
same manifold possibility of responding as to the sound 
of the same word, the time limit of preserving the generali- 
zation depends no longer on the delicate properties of his 
nervous system, which is so easily influenced by new 
experiences as well as by normal and abnormal physical 
processes like fatigue and disease, but on the physical 
properties of the material on which he has written the 
word. It is true that, quite recently, one has learned by 
phonographic records to preserve even the spoken word. 
But the limitations of this method are obvious, and, 
whatever may be its significance for the future, in the past 
at least the individual has had to depend for the preserva- 
tion of his generalizations on the written word, the memo- 
randum-book. Of course, we use here and in the follow- 
ing the term "word" in a very wide sense, including there- 
in all written symbols of any kind, especially those of 
mathematics, even all kinds of geometrical drawings, and 



220 HUMAN BEHAVIOR 

the diagrams and symbolic letters of physics, chemistry, 

and all other sciences. 

Secondly, we stated that by the substitution of the 
written for the spoken word communication of the indivi- 
dual's generalizations to other individuals has transgressed 
almost all limits of space and time. As we read a letter 
despatched from the opposite side of the globe, we learn 
what generalizations were most powerful in the nervous 
system of the individual who signed the letter, at the 
time — weeks ago — when it was written. As we peruse the 
book of an author long since deceased, we learn what 
generalizations of his own he thought desirable to commu- 
nicate to his contemporaries and those wdio were to live 
after him. As we uncover the tombs of the Egyptian 
kings, we learn what generalizations chiefly determined 
their actions thousands of years ago, while they were 
preparing for the common destiny of all individual life, 
for death. Posterity, opening our books, may learn what 
generalizations affected our nervous system so strongly 
that, in addition to using them in our individual life, we 
had them reproduced in the printer's office. Thus all 
mankind becomes a unit, spatially and temporally. The 
individual's experiences are no longer useful to him and to 
the few people of his direct environment alone. All 
other individuals of the present and future may profit 
by them. Thus only, mankind becomes in the world 
of animal life that power the vastness of which nothing 
perhaps testifies as much as the existence of poetry and 
religion. But to the grow T th of this power neither poetry 
nor religion contributes directly. Its systematic further- 
ance is the task of science. Science is the sum total of 
all those generalizations which the experience of mankind 
has invented, selected, and collected as the most useful 
for the control of the muscular response called forth by 
sensory excitation . 



SCIENCE 221 

The statement of the last sentence calls for further 
elaboration since the work of a scientist, especially to 
those not very familiar with it, seems to be altogether 
different from that of the ordinary man, say, the farmer 
plowing his field, — seems to belong to a category of activity 
other than that of motor (muscular) response to sensory 
excitation. 

When, in the evolution of civilization, the writing of 
words and other symbols of generalization has firmly 
established itself in a sufficiently large group of men, in 
a tribe or a nation, the written symbols become a special 
class of important objects to which, however artificial 
their origin, man has to learn to respond in order to be 
successful in the struggle for life, as formerly he had to 
learn to respond to those objects alone which have their 
origin in nature. Moreover, young people selecting 
a class of objects to which to devote their lives as specialists 
may now not only select from the natural objects, but may 
choose even this class. Their life work, then, consists 
in responding to written symbols by writing symbols and, 
of course, also by pronouncing them, as in oral teaching. 
The scientist's work, aside from experimenting, that is, 
testing the value of his generalizations by skilful appeals 
for an answer to nature, consists in combining, on writing 
paper, symbols already existing into new groups and in- 
venting for each group of generalizations which has been 
demonstrated by experiment to be a useful combination of 
symbols, a new name, that is, a new symbol of generaliza- 
tion. All this is, clearly, motor activity in response to 
sensory excitation. The only distinguishing features 
are these, that the scientist's motor activity does not 
require muscles of any great strength, and that it does 
require an enormous amount of learning, of variations of 
response, before it can begin to be of any value to humanity. 



HUMAN BEHAVIOR 

Let us take an example from the most ancient of all the 
sciences, which, notwithstanding its age, is still and will 
always be the foundation of all others, — from arithmetic. 
No one doubts that the most ancient symbols for larger and 
smaller groups of things were diagrams of familiar objects. 
The Roman numerals V and X, for example, are dia- 
grams of one hand with fingers spread out and of two hands 
united in opposite positions at their wrists. Even if these 
diagrams, originally, signified only a quantity portable 
in one hand and a quantity portable in both, they would 
already be generalizations, for many are the things or 
substances which can be carried by hand. If not at once, 
at a later period, these diagrams came to signify five 
and ten. They are then a step further removed from 
natural experience; they have assumed to a further degree 
the meaning of a generalization (or, if you prefer, of an 
abstraction). When a person counts, up to five or any 
other number, he enounces in regular order one of the words 
of a series which he must previously have learned, while he 
removes to a position of repose, say, w T ith his finger on the 
table, or with his turning eye in the subjective field of 
vision, just one more each time of the objects counted. 
The series of words spoken in doing this (that is, the series 
of numbers) is a generalization since it represents innumer- 
able different manners of successively removing the objects, 
only two of which (by the finger and by the eye) have 
been mentioned above. When written symbols like our 
Arabic figures are substituted for the spoken words, new 
generalizations are made possible. What is the sig- 
nificance of the plus sign? If we write it in 7+8, we invite 
the reader to count a group of seven things of his own 
choice and another group of eight as if they were only a 
single group of countable things. The plus sign, 
then, is a generalization for any kind of sensori-motor 






ARITHMETIC 223 

activity arranging the things as if they were a single series 
and counting them thus. The minus sign is a generalization 
of a similar kind. In 7—4, for example, we express the 
question: How many times more do you count after 4, till 
you enounce 7? The minus sign, then, is a generalization 
for any kind of sensori-motor activity arranging the 
things of one series as if they were two series. The mul- 
tiplication sign presupposes the experience of the plus 
sign. By writing 3X7 we invite the reader to perform 
the work of adding 7 plus 7 plus 7. Modern mathema- 
tics has greatly increased the number of such generali- 
zations, — think only of logarithms, not to mention higher 
mathematics. Yet by degrees they can all be reduced 
to the relatively simple sensori-motor activity of counting 
a series of things. 

Another example of a scientific generalization might 
be taken from mechanics. Remember the formula 3^2^^ 2 ? 
generally used in measuring our experience of "force." 
Man, in his intercourse with nature, learns how to resist 
moving objects and also how to utilize the motion of ob- 
jects (a hammer, for example) for his own purposes. He 
learns that he has to exert more muscular energy if the 
object resisted is heavier, and also that his work is more 
effective if he uses a heavier tool. He generalizes his 
experiences of resistance to objects and of work by the aid 
of objects — experiences to which he has already given the 
general name of " force " — by pronouncing the word " mass " 
in order to express their quantitative aspect. In writing 
this word he abbreviates it by writing simply m. By 
further experience man learns that he has to exert more 
muscular energy and also that his work is more effec- 
tive, if the object in question moves more quickly. 
These experiences, in addition, he generalizes in writing 
by uniting the symbols "mass" and "velocity" in a single 



224 HUMAN BEHAVIOR 

formula, connecting them by a sign of multiplication. 

At our present time, however, one does not write simply 
ffiXf, but mxtr , multiplying v with itself. This is done 
because the formula mxv , in algebraic relations with other 
formulas expressing other important experiences with 
heavy bodies, is in general more convenient. Still, this 
greater convenience was only gradually recognized 
by scientists. Two hundred years ago the question was 
debated in heated controversies between the most distin- 
guished scientists whether the symbol mv or the symbol mv 2 
was a more useful tool of generalizing human experience, 
or, as they expressed it, — talking as if force were a measur- 
able thing among the other objects in nature, instead of 
a mere generalization invented by man — "whether 
force was proportional to velocity or to the square of 
velocity." 

At present the latter formula is generally preferred, 
but slightly modified by the addition of the factor 3^2- 
This simplifies again the algebraic operations, for the for- 
mula }/2rnv can be put down directly as equal to a certain 
other very important formula of mechanics. The useful- 
ness of the equation thus formulated is the only reason 
why our scientists have become accustomed to using 
exclusively the formula yfanv in their generalizations of 
the quantitative aspect of the qualitative generalization of 
"force." (We may mention, by the way, that the use 
of the equation in question gradually brought about a 
change of name of the generalization %mi? 9 so that it is 
nowadays called "work" in the text-books of physics.) 

Force, therefore, is by no means, as some speculative 
philosophers would make us believe, a reality given by 
nature, and truly measurable only by a single formula, 
but a men 4 abstraction created by man to suit his needs, 
and expressed by thai combination of algebraic symbols 



WORDS AND THINGS 225 

which best suits his needs, practical and theoretical, — - 
an abstraction from experiences so varied and complex 
that without this generalization we could not respond to 
the quantitative aspect of any one of them with any defi- 
niteness, we could not measure them. 

In school and all through life we find ourselves compelled 
to respond to traditional audible and visible symbols of 
generalization as well as to the situations presented by 
nature. We gradually learn to respond to these kinds 
of stimulations most successfully: we acquire scientific 
habits. An example of a habit of responding to symbols 
of generalization — or rather an example of a large group of 
such habits — is the multiplication table. To the phrase 
"seven times nine" we at once add, by habit acquired, 
the word "sixty-three," without having first to do any 
counting, thus saving a large amount of time. In a 
similar way one learns, long before he acquires the 
multiplication table, to combine words into sentences and 
sentences into periods, and to draw conclusions expressed 
in further sentences, without first having to devote time 
and energy to perceiving the things which are meant by 
those generalizing words and sentences. The enormous 
advantage of substituting this handling of words for the 
cumbrous handling of things is clear enough, but the 
danger of speculation is clear too, — the danger of combining 
words and of thus drawing conclusions, that is, of expect- 
ing the things to agree with the last group of words 
manufactured by us, for no better reason than this, that 
we know our succession of sentences to have been construc- 
ted according to the rules of grammar, syntax, and logic. 
This danger does not exist in the case of the multiplication 
table. Here, in our most elementary quantitative generali- 
zations, things always agree indeed with our conclusions. 



226 HUMAN BEHAVIOR 

But our purely qualitative generalizations are so inexact 
that the things, when we perceive them, often turn out to be 
quite different from what we, guided only by our habits 
of handling words, expected to find them. 



SEVENTEENTH LECTURE 

The generalizing function changing from a nervous and 
muscular into a purely nervous function. Relation between 
processes in the higher nerve centers and strictly subjective 
experiences. Nervous functions of generalization especially 
likely to have also the subjective aspect. For the generalizing 
nervous function in another person's brain we substitute 
an imaginary mental state. The nervous correlates of sensa- 
tion and imagery. Associations of successive and of simul- 
taneous mental states. Attention. Pleasantness and un- 
pleasantness. Insufficiency of introspective psychology. 

WE have discussed, in some detail, the 
biological significance of spoken and 
written language. We stated that prac- 
tically no generalization is possible with- 
out speech. We showed that generalization, regarded as 
a biological function, comes about by the insertion of an 
additional link in the series of organic processes previously 
existing, and that the link added is a double link, a motor 
response, speaking, and a sensory excitation, the sounding 
word. One must not conclude, however, that conse- 
quently in every process of generalization the subject 
must actually speak the word upon which this generaliza- 
tion is based, that is, must innervate and move his speech 
organs. No doubt, generalization in general has its 
origin in actual speech. But the speech function in all 
generalizations tends to change during use from a nervous 

Ml 



228 



IITMAN HKIIAVIOR 



and muscular function to a purely nervous function; and 
a highly educated individual may even originate generali- 
zations without at all calling his speech organs into play. 




S b Sc Sd Sw Nw ^ Mf M g 

Fig. 54 — Generalization without actual speech. 



Figure 54 helps us to understand the dropping out of the 
muscular function. The figure is a composite of Figures 
52 and 53. In discussing the latter figures we showed 
that an excitation by any article of food of any one of the 
sensory points to the left (in Figure 54) may call forth a 
response at any one of the motor points to the right by 
mediation of M w and S w , since the reaction at M w , the 
organ of speech, results in a sound and thus in a physical 
stimulation of S W9 the ear. 

In this way any article of food appearing before the 
eye or another sense organ tends to call forth any 
action of preparing for a meal and eating. Now, a glance 
at Figure 54 teaches thai the generalization, as soon as 
established, no longer needs the peripheral points S w and 
M w , essential to its creation. A nervous excitation start- 
ing from S a , S b , S c , or S d can directly over Sl hcdw M efghw 
take its path to M e , M f , M gy and M h . The functional 
relation to the points S w and M w of this direct path is then 
merely historical, consisting in the fact that a part of the 
path from, say, S a to M h (namely, the part from the point 



THE OBJECTIVE— THE SUBJECTIVE 229 

Sabcdw to the point M e f ghw ) has in the past been traveled over 
by nervous processes coming from S w . A fact of this kind 
we shall soon find to be of a particular significance. 

We have just seen that no actual speaking, nor writing 
either, is required for the functioning of a generalization 
once established. The biological function of generaliza- 
tion may be regarded as purely nervous. Moreover, it 
is a nervous process inevitably taking its path over 
higher — very high — nerve centers. Between nervous pro- 
cesses in the higher nerve centers and strictly subjective 
experiences, that is, the individual's states of consciousness, 
there is an important relation. We have good reason to 
believe that a mental state never occurs unless there is at 
the same time a nervous process taking its path through 
the higher nerve centers. It is probably not correct to 
call the relation between a mental state and a process in a 
higher nerve center causal, which would mean that the 
one occurs first and the other after, or the other first and 
the one after. More probably they are strictly simultan- 
eous; but we are as yet unable to prove it because science 
has not yet invented an instrument by means of which we 
can observe the process going on in our own brain while 
we have the mental state corresponding to it. If they are 
strictly simultaneous, we have the right to describe them 
by saying that they are really only one phenomenon 
occurring in the world, but that this phenomenon has two 
aspects. In so far as it can be observed by any and all 
individuals, including the one whose brain is affected, 
who are in possession of the proper instruments (not yet 
invented), we call it an objective phenomenon, a nervous 
process. In so far as it is (and can be) known exclusively 
by the one individual whose brain is affected, we call it a 
subjective phenomenon, a mental state. We understand, 
then, that among all the possible nervous functions those 



280 HUMAN BEHAVIOR 

of generalization are especially likely to have also the 
second, the subjective aspect, because they occur in very 
high nerve centers. 

This brings us back to the considerations with which 
we started out in the first lecture. We stated there that 
in pronouncing a moral judgment on a boy who has 
obstructed the track of a train, we seem to be interested 
chiefly in his thoughts, although only his actions, never 
his thoughts, can be known to us by observation. When 
in school, we seem to be interested chiefly in what our 
teacher thinks of us, although only his actions can be 
observed by us. The path is now open for our under- 
standing this. 

The proper valuation of the boy 's or the teacher 's action 
depends on the application of the proper generalization. 
It really does not matter much whether the boy placed 
a plank on the track by using his hands, or caused a 
rock to roll on the track by using his feet, or, by using 
his speech organs to pretend a different purpose, made a 
friend put a stick of dynamite there. What matters 
is only the fact that all these events are likely to 
cause the derailment of a car. The derailment, again, 
is not of so much importance for our judgment as the 
fact that the derailment may be the cause of many differ- 
ent events, the saving of a train from passing on a bridge 
with underwashed foundations, the killing and maiming 
of numerous passengers by the destruction of the car, and 
innumerable others. Our judgment, then, is impossible 
without generalization. It is itself a generalization of a 
high order. It expresses our decision as to what generaliz- 
in g function determined the boy's motor activity, whether 
he said to himself (remember in Figure 54 the points M w 
and S w \): "I will save" or "I will kill." 



SUBSTITUTION OF A MENTAL STATE 231 

As we found in the preceding lecture, however, it is not 
necessary that the boy actually pronounces the word. 
It leads to the same motor result if the particular generaliz- 
ing function on which our judgment has decided, is purely 
nervous, a nervous process passing through a certain 
higher center in the boy's brain. Therefore, if our judg- 
ment were in every respect what it ought to be according 
to the standards of exact science, it would plainly express 
that this generalizing process occurred in this high center 
of the boy's nervous system. But, unfortunately, these 
nervous processes in the higher centers are only hypotheti- 
cal, owing to the fact that the instruments for their ob- 
servation have not yet been invented. That they will have 
been invented in a hundred years, or sooner, or later, 
does not help us. So we help ourselves by substituting 
in our imagination for the boy's nervous process which 
today the undeveloped state of physiology will not let us 
know, an assumed reality which we do not, shall not, 
cannot ever know, a mental state of the boy, his willing to 
save, or to kill. The right to substitute this assumed 
mental state, in spite of its being forever unknowable, 
for the nervous process, which is insufficiently known 
only because of the insufficient development of scientific 
technic, we derive from the fact that a (slightly familiar) 
nervous process like the boy 's is in each of us, individually, 
regularly coexistent with a perfectly familiar state of 
willing to save or to kill. 

In a similar way we substitute in our imagination for 
the nervous process determining our teacher's actions a 
mental state taken from the store-house of our subjective 
experiences. Objectively, scientifically, we know only 
our teacher's actions. We are not so much interested, 
however, in the particular act as in the class to which it 
belongs. We do not, for example, care so much whether 



2S2 HUMAN BKHAVIOR 

he uses his writing hand or his talking mouth to praise us, 
as we care for the general fact that he praises us and does 
not blame us. It is, therefore, the generalizing nervous 
function in a high center of the teacher's brain that concerns 
us. And for this nervous function we substitute, for 
reasons stated, an imaginary mental state, — imaginary 
since, not being ours, it is unknowable to us. 

From this it must be clear that there can be little 
scientific progress in our knowledge of the interrelations 
between human beings until we shall be able to compre- 
hend better the nervous processes of generalization which 
almost exclusively determine these interrelations, our 
social intercourse. But since we shall undoubtedly 
continue, for a long time to come, to substitute in our 
discussions of social events for the generalizing nervous 
processes imaginary mental states, it is important that 
we understand how T in our individual life nervous processes 
and mental states are connected. We emphasized on 
page 20P that (in Figure 54) a part of the path of the 
generalizing function had in the past been traveled over 
by nervous processes coming from S w . Let us note that 
stimulation of S w is stimulation by a word, and let us 
remember the extraordinary part played in any generalizing 
function of our individual consciousness by word imagery. 
We draw the conclusion that our consciousness of the 
word-image, when any of the points S a , S b9 S c , or S d in 
Figure 54 is stimulated and responded to by any of the 
points M g , M/, M g , or M h , has its nervous correlate in the 
fact that a part of the nervous path taken by the excitation 
has previously been traveled over by a nervous excijtation 
coming from the sensory point S w corresponding to the 
particular nature of this word image (auditory, visual, 
etc.), while S w remains at present unstimulated. 



CORRELATES OF MENTAL STATES 233 

Thus we can at once establish a general rule concerning 
the nervous correlate of sensation, on the one hand, and 
of imagery, on the other. Sensation, we know from our 
individual experience, requires proper sensory stimulation, 
but requires also, we have good reason to believe, that 
the nervous excitation takes its path, not directly over 
a reflex arch, but over higher nerve centers; otherwise 
there is no consciousness. It is a common condition, 
then, for the existence of either sensation or imagery, 
that the nervous process does not remain in the lowest 
centers, but takes its path over higher nerve centers. The 
difference, whether our consciousness is a sensation or an 
image, depends on this: If the nerve center which is 
conducting a nervous excitation, is at present serving the 
sensory point corresponding to the mental state in question, 
that mental state is what we call a sensation; if the center 
has only in the past served the sensory point corresponding 
to the mental state in question, that mental state is what 
we call an image. 

Introspective psychology, that is, the psychology which 
restricts its observations to (the observing individual's) 
consciousness and attempts to comprehend human life 
by comprehending the one individual's life, has long ago 
formulated one important law, that of the association 
of mental states. An association may be one of successive 
or of simultaneous mental states. In the former case, 
"association" means that the particular mental states 
tend to recur in the same order, or, more rarely, in reversed 
order. In the latter case, "association" means that the 
particular mental states tend to occur together at one 
moment rather than temporally separated from each other. 
Let us state, in the terms of nervous function employed 
in these lectures, the nervous correlate of the law of 
association. 



284 HUMAN BEHAVIOR 

A nervous process starting from a certain sensory point, 
say, S fl in Figure 16, terminates and is succeeded by another 
nervous process starting from S b . This second process 
is then not uninfluenced by the first. A larger fraction 
of its flux takes its path over the connective neuron S% b 
Mj b than would have done so if the other flux had not a 
moment ago been conducted partly by this neuron. (We 
have discussed this same fact in Lecture 10 with a 
somewhat different end in view, namely, in order to show 
that a nervous process can be more or less deflected not 
only by a simultaneous stronger one, but also by any directly 
preceding one.) When now, at any later time, S a is stimu- 
lated again, more of the flux passes up from Si to S 2 ab M 2 ab 
than the first time, since the resistance of the higher center 
S 2 ab M 2 ab , affected by two nervous processes, has been re- 
duced relatively more than that of the lower center S\M \. 
If we represent by S l a M \ a relatively high center, (relative 
to the whole system), the flux in S\M l a must be ac- 
companied by consciousness. The nature of this con- 
sciousness is determined by the nature of the sensory 
excitation at S a . The flux in the still higher neuron 
S 2 ab M 2 ab is accompanied by the same consciousness, but 
also by the consciousness corresponding to the nature 
of the sensory excitation at S b , because S ab M ab has been 
traveled over previously by a nervous process coming from 
Si,. It is clear that the mental state "b" must begin 
Inter than the mental state "a" since the relief of tension 
starting from S a can not reach the point S% b as soon as 
the point S\, The successive association of the two 
mental states is therefore a simple consequence of our 
assumptions concerning the laws of nervous function. 

What we have just said about two mental states of a 
successive association, holds equally for three, four, etc. 
Nothing new is to be found in these cases, except that, the 



ASSOCIATION 235 

greater the number of different sensory excitations (for 
example, add S c and S d in Figure 16), the higher are the 
nerve centers coming, more or less, into play (up to 
Sabcd Mabcd in the same figure). This is evident enough. 
Another fact, however, deserves probably a brief discus- 
sion, that of reproduction of the mental states in the order 
opposite to the one in which they were acquired. The 
classic treatise of Ebbinghaus "On Memory" proves the 
existence also of a tendency for reproduction in the 
reversed order. The nervous correlate of this tendency 
is easily derived from the same example which we have 
just used. If S b alone is stimulated, after the succession 
of stimulus "a" and stimulus "b" has had its opportun- 
ity for changing the relative resistances of the higher 
centers in Figure 16, the nervous excitation travels, not 
only over S } b Ml but also considerably over S 2 ab M 2 ab . 
The flux in the centers S b M b and S ab M ab is then accom- 
panied by two mental states, "b" occurring first because 
the center SlMl can be reached from S b in less time than 
SabM^ That is, the mental state "b" calls up the 
mental state "a" although in all the instances of twofold 
stimulation "b" was invariably preceded by "a." 

Ebbinghaus rightly points out, however, that this re- 
production of mental states in the order opposite to that 
of their acquisition by the individual is quite rare. He 
explains it by calling attention to the fact that, as a rule, 
the two mental states are members of a series and are 
followed by other mental states. In the alphabet, for 
example, "b" but rarely calls up "a," because its tendency 
to call up "c" is still greater. Let us explain the same 
fact in terms of nervous function by the aid of Figure 55. 
If in the mental process of memorizing the letters of the 
alphabet or any other series S q is stimulated soon after a 
flux from S p has occurred in the center S 2 q M 2 q , the part 



236 



HUMAN BEHAVIOR 



of the flux which does not take its path from S% to the 
right hut upwards, must divide so that more passes in 



the direction of S^ and over the center S Pq M Pq than 



3 PQ 



f2 

l p( 



in the direction of S qr and over the center S qr M qr . 



We 



may say, then, that from any of the points S 1 a larger 




Cip rip o q riq S 7 M 7 

Fig. 55 — Two directions in successive association. 

flux travels up to the left than up to the right. This is 
indicated in Figure 55 by double and single lines. It is 
then immediately clear that during the memorizing any 
one of the neurons marked S M receives from the right 
below a stronger flux than from the left below. For 
example, $ 2 Pq M 2 Pq receives relatively a strong flux from 
Sgj a weak flux from S p ; and S 2 qr M 2 qr receives a strong flux 
from S n a weak flux from S Q . On some later occasion S q 
alone is stimulated, say, for the sake of a test. The flux 
divides at S\. A part travels over S\M\, another part 
over S 2 Pq M 2 Pq , a third over Sl r M qr . Our problem is to 
show whether of the mental states other than "q," namely 
"p" and "r," the one or the other has a higher degree of 
consciousness. Obviously, the degree of consciousness 
depends on the relative flux which has previously passed 
over the higher centers S 2 pq M 2 Pq and S 2 qr M 2 r from S P 



ATTENTION 237 

and S r . Above we found that the previous flux over the 
higher centers from S r was relatively strong, from S P rela- 
tively weak. Accordingly, the mental state "q" tends to call 
up the associated mental state "r" rather than the associ- 
ated state "p." Thus we have explained this rule of 
introspective psychology in terms of nervous function. 

To explain in terms of nervous function the simultaneous 
association of mental states, it is only necessary to refer 
to our discussion of that kind of variation of the nervous 
path which we called motor condensation. If a number 
of sensory excitations unite in a higher center in order to 
pass into a common motor outlet, the condition for a 
simultaneous association of definite mental states is 
fulfilled. Whenever now, even from a single sensory 
point, a nervous process travels over that center, the 
mental states corresponding to all those sensory excita- 
tions must simultaneously enter consciousness. 

Aside from the time-honored law of association, only 
one other generally recognized law of mental life has been 
discovered by purely introspective psychology, the law 
of attention. By attention is meant "the peculiar fact 
that of a great number of conscious impressions or ideas 
simultaneously offered to the mind, only a few can ever 
be carried through and become effective." It is plain 
that, in terms of nervous function, this is the law of 
deflection of weaker nervous processes by a stronger one. 
The stronger nervous process determines the dominant 
aspect of the total mental state. The weaker ones, if 
deflected from their own course before having reached 
any centers of a higher level, are not accompanied by any 
consciousness whatever. The higher the center reached 
by any of these nervous processes before it enters the 
path of the stronger process, the more pronounced, 
relatively, the corresponding consciousness; the greater, 



238 HUMAN BEHAVIOR 

obviously, also its chance of becoming later the prevailing 
nervous process itself and determining the animal's next 
action. Thus we must expect to find by introspection 
in our individual mind as a rule a single mental state 
dominant together with a large number of others of vary- 
ing degrees of consciousness. The law of attention, which 
has caused introspective psychology so much discomfort, 
and which Herbart attempted in vain to clear up by his 
"mechanics of ideas," thus becomes clear enough as 
soon as we comprehend its nervous correlate. 

Introspective psychology has long struggled to under- 
stand the relation between the feelings of pleasantness and 
unpleasantness (not meaning by the latter term "pain," 
which is a sensation) and human behavior. It seems ad- 
visable to approach the problem from another point of 
view, studying objective nervous functions, hypothetical 
as they may be for the present, rather than the intro- 
spections of the individual which by their very nature 
can never be anything but subjective. We can distin- 
guish two classes of conflict between two nervous processes 
of which one originates while the other is still going on. 
Either, the first is stronger, deflects the second and by 
absorbing it grows still stronger. This corresponds to 
our experiences of pleasantness, for in all such experiences, 
however varied in other respects, we continue the same 
form of behavior more and more vigorously. Or, the 
second nervous process is stronger, weakens the first by 
deflection, and finally absorbs it completely. This cor- 
responds to our experiences of unpleasantness, for in all 
such experiences our behavior suffers interference until 
it i> completely replaced by another form of behavior, 
when the unpleasantness ceases. The nervous correlate 
of feeling may then be described in the following words. 
The nervous correlate of -pleasantness and unpleasantness 



PLEASANTNESS— UNPLEASANTNESS 239 

is the increase or decrease of the intensity of a previously 
constant nervous process if the increase or decrease is 
caused b} r a force acting at a point other than the point of 
sensory stimulation. The condition of the second half 
of this sentence is necessary because our experiences of 
feeling do not depend on a change in the intensity of a 
stimulus, but on the interference of nervous processes in 
higher nerve centers. 

Introspective psychology, disregarding behavior, for cen- 
turies has been satisfied with remarking that pleasant 
experiences are the experiences of helpful situations, 
unpleasant ones those of harmful situations,. This is true 
enough, for the animal body is so equipped by nature with 
nervous connections of sensory and motor points that 
reactions to a helpful situation continue and grow stronger, 
reactions to harmful situations are weakened until they 
discontinue. But there are exceptions to this rule which 
destroy its whole value for any mental or social science, 
for it is an undeniable fact that the pleasure-seeker may 
sacrifice his life to pleasure. Not the study of the in- 
dividual's consciousness, of "the structure of the mind," 
but the study of the nervous laws of behavior will enable 
us to understand the significance of human action for 
human life in the individual and in society. The scientific 
value of introspective psychology consists merely in the 
fact that it aids us in discovering the laws of nervous 
function.* 

How unreliable the results of introspective psychology 
are, can be learned, for example, from the attitude of 

*A more detailed account of the relations between mental states and 
nervous functions may be found in my articles "The Nervous Correlate 
of Pleasantness and Unpleasantness" and "The Nervous Correlate of 
Attention," Psychological Review 15 y 201-216, 292-322, 358-372; 16, 36- 
47. 1908-9- Compare also an elaboration of this theory and appli- 
cation to sociology by L. L. Bernard, "The Transition to an Objective 
Standard of Social Control," The University of Chicago Press, 1911. 



240 HUMAN BEHAVIOR 

psychologists toward the question as to the relative 
importance of the kinesthetic sense. When, during the 
nineteenth century, sensory neuron endings were dis- 
covered in muscles and tendons, some psychologists made 
use of the new sense in order to explain numerous pheno- 
mena whose explanation had formerly been impossible. 
Immediately they were opposed by others who asserted 
that the kinesthetic sense was of practically no significance 
since in their individual consciousness they could not, 
introspectively, discover any kinesthetic sensations or 
images at all. We saw in Lecture 13 that kinesthetic 
sensory' activity is quite indispensable for the training of 
any temporally complex reaction, for example, speech. 
Introspective psychologists, however, are rarely among 
those people who — like mechanics, skilled factory workers, 
sportsmen, and athletes — acquire new habits of temporally 
complex reaction late in life. Their own habits of this 
kind were all acquired in early childhood and have long 
ago become completely automatic, — short-circuited, so 
to speak. Since the nervous processes of these reactions 
no longer pass over higher centers, there can then be little 
consciousness, especially no consciousness of kinesthetic 
sensation or imagery. It does not follow, however, that 
this consciousness was absent in their first few years of 
life when they received all the motor skill they possess; 
and it does not follow that the kinesthetic sense during 
any period of life is insignificant as a nervous function. 
This is, perhaps, the best example one can find of the 
failure of introspection in the explanation of human 
behavior. 

Enormous is the amount of introspective research 
embodied in the publications belonging to the mental and 
social sciences from Aristotle to the present day, enormous 
the energy which has been spent on careful analysis of 



INTROSPECTIVE PSYCHOLOGY 241 

introspective records by the application of generalizations, 
of abstractions. But if one attempts to collect results of 
these investigations which are generally recognized — 
or recognized at least by a majority of the scientists of the 
present day — as contributing toward an understanding of 
human life in the individual and in society, he is struck 
by the fact that there is almost nothing to be collected. 
A few abstractions are recognized as valuable for the 
science of general psychology: memory, association, 
attention. In the special mental sciences, ethics, 
education, sociology, politics, political economy, little — 
aside from purely statistical facts — seems to be more than 
personal opinion. There appears to be only one hope 
that a real mental and social science, comparable to natural 
science, will ever come about, the hope based on the 
observation that just as far as the facts and laws of 
introspective psychology have hitherto been correlated 
with — replaced by — facts of behavior and its laws, has 
confusion and obscurity given place to order and clearness 
in the mental sciences. There is hope, then, that by future 
progress in our knowledge of the laws of human behavior 
more order and clearness will be there introduced. 






TRANSLATIONS 

Adolf Hildebrand, The Problem of Form in Painting 
and Sculpture; translated and revised with the author's 
co-operation by Max Meyer and Robert Morris Og- 
den. G. E. Stechert & Co., New York. 90 cents net. 
The famous sculptor of Munich, Germany, describes 
in this book the mental processes which dominate his 
own artistic activity. 

Hermann Ebbinghaus, Psychology; translated and edited 

by Max Meyer. D. C. Heath & Co., Boston. $1.25. 

An introductory text for college students and general 

readers. Easily readable, up to date, comprehensive. 

Adapted to one semester courses. 



NOV 25 1911 



One copy del. to Cat. Div. 



;.i91l 



